中国东南假等称笔石(Pseudisograptus Beavis)

SOME SPECIES OF PSEUDISOGRAPTUS BEAVIS FROM SOUTHEAST CHINA

假等称笔石(Pseudisograptus)是Beavis(1972)重新研究澳大利亚维多利亚州(Victoria)等称笔石时,根据Isograptus manubriatus的标本所建的属,其模式种为Didymograptus cauduceus var. manubriatus T. S. Hall。这个属的特征是:1)剑柄构造(manubrium)的始部构造,由始部胞管起源明显地集中在胎管区而形成;2)始部胞管弯曲,开口向外;3)具简单的原胞管褶。这个属包括Isograptus manubriatus, I. hastatus, I. dumosus (Beavis, 1972)。Pseudisograptus manubriatus是一个非常特殊的种,其形态变化范围很广。

Some well-preserved flattened and relieved specimens of Pseudisograptus collected from the Lower Ordovician Ningkuo Formation (Arenigian) of Yushan, eastern Jiangxi and Jiangshan, western Zhejiang are described as Pseudisograptus manubriatus harris, P. manubriatus koi, P. manubriatus ianus, P. bellulus, P. sp. and P.? zhejiangensis. Among them, P. manubriatus harris and P. manubriatus koi are reported for the first time from China, while P. manubriatus harris even has never been found outside Victoria of southeastern Australia before; the type specimens of P. jiangxiensis and P.? zhejiangensis are redescribed in this paper.In China, the genus Pseudisograptus has also been recorded from Huocheng of N. Tianshan (described as Isograptus dumosus by Xu and Huang, 1979) and Xing'an of N. Guangxi (listed as P. hastatus by Chen and others, 1981).Family uncertain Subfamily Pseudisograptinae Cooper et Ni, 1986Remarks: This subfamily is considered by Cooper and Ni (1986) as belonging to the family Glossograptidae because the morphologiical gap separating glossograptids from Pseudisograptus was much narrower than formerly thought and the ancestor of the glossograptids was most likely a pseudisograptid. However, the glossograptids usually have one or two pairs of pendent thecae at the proximal end as in isograptids, while in Pseudisograptus the proximal thecae show a marked outward deflection. This appears to imply that the origin of glossograptids may be lsograptus rather than Pseudisograptus. For the time being, it seems that the family which the Pseudisograptinae should be long to still remain uncertain.Genus Pseudisograptus Beavis, 1972 (=Arienigraptus Yu et Fang, 1981; =Xiushuigraptus Yu et Fang, 1983)Type species: Didymograptus caduceus var. manubriatus T. S. HallPseudisograptus manubriatus harris Cooper et Ni (P1. Ⅰ, figs. 2, 4)1933 lsograptus manubriatus (T. S. Hall) (pars), Harris, pp. 102—104, ?pl. 6, figs. lb, g, i; text-fig. 44 (non pl. 6, figs. la, c, d, e, f, h; text-figs. 41—43).1986 Pseudisograptus manubriatus harris, Cooper and Ni, pp. 331—332, p1. 25, figs. 9, 13; text-fig. 11.Material: 2 flattened specimens.Description: Rhabdosome relatively large, U-shaped, about 9mm in length and 7mm in width. Two stipes nearly parallel, diverging at 3300--340~, about 6 mm in length and 2.2 mm in width. Manubrium 2.5—2.7 mm long and 1.5—1.8 mm wide, with the angle subtended by manubrium at 30°. Sicula 8 mm long, with free proximal portion about 0.2 mm in length. Infradorsal region 3.0—3.2mm long.Proximal development and construction of manubrium invisible in the present material. Thecae straight, with gently concave apertures, inclined at 20°—30°from dorsal margin, numbering 5 in 5 mm.Horizon and locality: Zone of Cardiograptus amplus, Yushan, E. Jiangxi.Pseudisograptus manubriatus koi Cooper et Ni (P1. Ⅱ, figs. 1, 3, 4; P1. Ⅳ, figs. 1, 2, 6; text-figs. 3A—c)1973 Isograptus manubriatus (pars), Cooper, pp. 84—88, text-figs. 22a—g, 1—n, p(non h—k, o, q).1974 Isograptus manubriatus, Tzaj, p. 94, p1. 9, figs. 11—15 (non figs. 7—10); text-fig. 29.1979 Pseudisograptus manubriatus Form B and D, Cooper, pp. 78—79; p1. 15, figs. a—c, f, g; text-figs. 60a, b, d (non pl. 5. fig. h; text-fig. 60c).1986 Pseudisograptus manubriatus koi Cooper et Ni, pp. 332—339, pl. 24, figs. 1—6, 9—12; p1. 25, figs. 3, 4; textfigs. 12a—d and 13A—G, J.Material: 20 flattened, 2 partly relieved pecimens.Description: Rhabdosome usually small and anchor-shaped, with two reclined stipes. Sicula averaging 5.6 mm (range 4.5—6.6 mm), with free proximal portion averaging 1.8mm (range 1.5—2.3 mm) in length. Manubrium averaging 1.8 mm (range 0.8—2.4 mm) in length and 1.7 mm (range 1.3—2.1mm) in width. Angle between shoulders of 40°—50°. Infradorsal region averaging 1.9 mm (range 1.5—2.1mm) in length. Distal thecae of low inclination (20°), in advanced manubrium form.Immature rhabdosome dumbbell-shaped. Proximal development and construction of manubrium. known only from a single specimen (P1. Ⅱ, fig. 4) which shows the reverse side of the middle part of the rhabdosome preserved in relief. Sicula about 6.5 mm in length; free sicula portion 2.4 mm in length, with a nema about 4 mm in length- Thl^1 originating at 0.5 mm below the top of sicula. Thl^2 arising from the reverse side of sicula at about 1.4mm below thl^1, growing nearly horizontally across the stipe^2 side of the rhabdosome before commencing its downward growth, and quickly giving rise to th2~1 which grows across and below the stipe^1 side. Th2~2 arising from the dorsal side of thl^2, forming a prothecal fold. Manubrium comprising the proximal portions at least the first three pairs of thecae beyound thl^1.Horizon and locality: Zone of Cardiograptus amplus, Yushan, E. Jiangxi.Pseudisograptus manubriatus ]anus Co)per et Ni (P1. Ⅰ, figs. 1, 3; P1. Ⅲ, figs. 1—3; text-figs. 3D—F)1973 Isograptus manubriatus (pars), Cooper, pp. 84—88, text-figs. 22h—k (non text-figs. 22a—g, 1—q).1974 Pseudisograptus manubriatus Form C, Cooper and McLaurin, pp. 77—80, text-figs, le—g (non text-figs. 1a—d).1979 Pseudisograptus manubriatus Form C, Cooper, pp. 78—79, pl. 15, fig. h; text-fig. 60c.1983 Xiushuigraptus songxiensis, Yu et Fang (in Yang and others), p. 407, p1. 149, figs. 11, 12; text-fig. 1.1986 Pseudisograptus manubriatus janus, Cooper and Ni, pp. 339—347, pl. 25, figs. 5, 8, 10—12; p1. 26, figs. 1—7; p1. 27; text-figs. 13H, J. 16, 17.Material: 9 flattened specimens and 4 relieved specimens.Description: Rhabdosome large, with two reclined stipes about 1.5 mm in width. Sicula very long, averaging 7.3 mm (range 6.8—7.7 mm) in length, with free portion averaging 2.3 mm (range 2.2—2.5mm). Manubrium generally large, 3.0 mm (range 2.8—3.2 mm) in length and 2.1 mm (range 1.9—2.1mm) in width on an average. Angle subtended by the manubrium at about 30°; infradorsal length averaging 2.3 mm (range 2.0—3.0 mm). Thecae of low inclination (20°—40°), with 5 in 5 mm.Nothing can be added to the proximal development and construction of the manubrium described by Cooper and Ni (1986) on the basis of the new material. In obverse aspect, first three pairs of thecae growing downward parallel to the sicula, flexing sharply outward near their distal ends; fourth pair overlapping the third and growing towards sicula before swinging outwards to form part of the diverging reclined stipes. On he reverse side of the rhabdosome growth paths of th2~1, th2~2, th3~1, th3~2 and (in holotype) th4~1 completely overlapping those of earlier thecae until approaching their distal ends, where they swing sharply away from the midline of the rhabdosome and clearly reveal their plaited arrangement. The type species of Xiushuigraptus, X. songxiensis, is only represented by two incomplete small specimens (text-fig. 3F), which are indistinguishable from the immature specimens of P. manubriatus janus. It is believed that X. songxiensis is a junior subjective synonym of P. manubriatus janus as suggested by Cooper and Ni (1986).P. manubriatus janus can be easily distinguished from P. manubriatus koi by the sizes of the sicula and manubrium and the morphological characters of growth stages (text-fig. 3).Horizon and locality: Zone of Cardiograptus amplus, Yushan, E. Jiangxi.Pseudisograptus bellulus Cooper et Ni (P1. Ⅱ, fig. 2; Pl. Ⅳ, fig. 5)1986 Pseudisograptus bellulus, Cooper and Ni, pp. 348—349, p1. 26, fig. 8; text-fig. 21.Maberial: 3 flattened specimens. Description: Rhabdosome generally small, with two reclined stipes diverging at 310°—320°, each 1.2—1.6 mm in width. Sicula 4.9—5.7 mm in length; free portion 1.7—2.1 mm, with a thin nema. Manubrium relatively short and wide, 1.5—1.9 mm long and 1.7—2.0 mm wide. Angle subtended by manubrium at about 50°.Horizon and locality: Zone of Cardiograptus amplus, Yushan, E. Jiangxi. Pseudisograptus jiangxiensis (Yu et Fang) (text-flgs. 4G, H)1981 Arienigraptus jiangxiensis, Yu and Fang, pp. 29—30, p1. Ⅰ, figs. 1, 2; text-fig. 3.1986 Arienigraptus jiangxiensis, Hart, pl. 1, figs. 2, 5.Description: Rhabdosome small and incomplete, without reclined stipes. Sicula of holotype 2.8 mm in length, which was unfortunately damaged during a later preparation (Yu and Fang, 1981). Base of manubrium not clearly defined. Reclined stipes barely developed. Manubrium at least 0.7—0.9 mm in length and about 1.8 mm in width. Angle subtended by the manubrium ranging from 70°to 90°.Thl^1 2.7mm in length, budding off very high from sicula (Yu and Fang, 1981, p. 30), and growing downwards parallel to the sicula for the greater part of its length, diverging only upon approaching to sicular aperture. Thl^1 and sicula completely obscure, such as the sicula in reverse view, except for its proximal and apertural extermities. Sicular and thl^1 apertures exposed because of pronounced curvature affecting the distal portion of thl^2 and th2~1, directing the aperture away from the sicula. Thl^2 dicalycal, giving rise to th2~1 and th2~2 approximately at the same level, as in the hirundo stage of the proximal end development. Initial part of th2~2 not clearly preserved. Line of junction represented by the contact between thl2 and th2~1 nearly overlapping that of the sicula and thl^2 on the reverse side of rhabdosome. Following the appearance of th2~1 and th2~2, growth of each stipe proceeding independently, with each theca budding off from the preceding one shortly after the origin of the later and possessing primitive prothecal fold. Aperture of the theca not preserved.Remarks: The description is given based on the original specimens deposited in Department of Earth Sciences, Nanjing University.From the present evidence available, P. jiangxiensis is closely related to P. geniculatus and both may belong to the same phyletic group in Pseudisograptus. The proximal end development and the arrangement of initial thecae are almost indistinguishable between both species, but quite di