Tamdaspis Lisogor的分类位置、异名及新种

FAMILIAL POSITION, SYNONYM AND NEW SPECIES OF TAMDASPIS LISOGOR (TRILOBITA, LATE CAMBRIAN)

1982年夏,笔者在检查湘西凤凰山江千公坪剖面时,采获一批晚寒武世三叶虫化石,其中包括本文记述的新种Tamdaspis brevilimbus sp. nov。Tamdaspis最初见于苏联哈萨克,为(1977)所建。其后相继在我国新疆(张太荣,1981)和安徽(仇洪安等,1983)发现。最近在哈萨克又找到一些新材料(Apollonov et al.,1984)。安徽的材料,经钱义元、仇洪安鉴定,认为是一新属,命名为Psiloyuepingia Qian et Qiu,1983。Tamdaspis是一个比较特征的刺尾虫类(ceratopygids)三叶虫(尽管尾部缺乏侧刺)。

Tamdaspis brevilimbus sp. nov., a new species of Tamdaspis Lisogor, 1977, is described and figured from the mid-upper part of the Shenjiawan Formation at Qiangongping, Fenghuang County, western Hunan. The new material proves the first record of Tamdaspis in Hunan and adds to the genus the morphology of the librigena, the hypostoma and the pygidial doublure. Psiloyuepingia Qian and Qiu, 1983 is considered to be a junior synonym of Tamdaspis. The genus is regarded as a ceratopygid and placed in the subfamily Macropyginae that is here referred to the family Ceratopygidae, according to Fortey and Chatterton (1988). Family Ceratopygidae Linnarsson, 1869 Subfamily Macropyginae Kobayashi, 1937 [=Iwanyaspidinae Kobayashi, 1962] Genus Tamdaspis Lisogor, 1977 [=Psiloyuepingia Qian et Qiu, 1983] Tamdaspis brevilimbus sp. nov. (Fl. Ⅰ, figs. 1—13; Text-fig. 1) Name Derived from Latin—brevis, short, and limbus, border, referring to the narrow (sag.) preglabellar area. Holotype Here designated, an incomplete cranidium, NIGP133838 (P1. Ⅰ, fig. 3). Diagnosis A species of Tamdaspis with glabella twice as long as wide, defined laterally by sinuous, subparallel axial furrows; palpebral lobe large, with width (tr.) more than half of that of glabella; preocular sections of facial suture strongly divergent forward; width (sag.) of preglabellar area equal to one-fourth of the length of glabella; librigena with genal spine and very broad lateral border furrow; pygidium with conspicuous and dense lirae. Description Cranidium with angulate anterior margin. Glabella large, rectangular in outline, moderately convex and slightly expanded outward in front of palpebral lobes, with a width of about 1/2 length. Three to four pairs of glabellar furrows: preoccipital furrow bifurcated, with the anterior branch deeply incised and anteriorly directed and the posterior one shallow and transverse; 2p gently impressed, isolated from the axial furrow; 3p short and faint, running inward and forward from the axial furrow; 4p very short and scarcely visible, lying slightly in front of the palpebral lobe. Bacculae very small; glabellar node lying sagittally between the posterior branches of the preoccipital furrow. Occipital furrow deep, with median part gently curved rearward. Occipital ring as wide (sag.) as the preoccipital glabellar lobe with an even lateral profile. Palpebral lobe large, semicircular in outline, nearly as wide (tr.) as glabella, well-defined by palpebral furrow. Preglabellar area short (sag.), occupying only 1/4 of glabellar length (exclusive of occipital ring), with concave preglabellar field and small, forward-dipping anterior border. Posterior part of the preglabellar field with a pair of triangular-shaped, raised areas. Preocular facial sutures divergent forward at an angle of about 110°, turning inward and forward rapidly across the border to meet one another sagittally. Postocular suture short, enclosing the transversely triangular posterolateral limb. Librigena triangular in outline, with narrow, gently convex lateral border and very broad lateral border furrow. Genal field triangular, markedly convex, with its anterior part united with the convexity in preglabellar field. Lateral and posterior borders merged at genal angle, continuously extending into genal spine. Hypostoma subcircular, with anterior body rounded and highly convex. Maculae deeply notched, immediately succeeded by a pair of small projections. Posterior body crescentic, gently convex, defined posteriorly by a shallow border furrow. Anterior wing small, triangular. Lateral border very wide (tr.), narrowing forward rapidly; posterior border narrow (sag.), with posterior margin gently sinuate. Pygidium twice as wide as long or even wider, with rounded anterior lateral corners. Axis highly convex, 2/3 as long as pygidium, and containing 5 rings, and a terminal piece which continues into a low postaxial ridge. Pleural field gently convex, with 5 segments, of which the last three bearing no pleural furrows and defined by broad and deep interpleural furrows, and the second segment composed of very narrow (exsag.) anterior band and evidently wide posterior band. Border slightly convex, defined by feeble border furrows. Doublure very broad, with V-shaped inner margin, bearing a conical convexity opposite the postaxial ridge on the dorsal surface. Prosopon visible on the hypostoma and the lateral border of the librigena as fine concentric terrace lines, on the pygidium as heavy, conspicuous, concentric terrace lines, and on the pygidial doublure as heavy, fine terrace lines parallel to the inner margin. Remarks Ten species have been described since Tamdaspis was erected (Lisogor, 1977; Zhang, 1981; Qiu et al., 1983; Apollonov et al., 1984). Among them, 4 species, T. cylindrica, T. toxeus, T. intermedia and T. sp. sensu Apollonov et al., may be conspecific. The holotype of the type species T. tamdensis with a forward-tapering glabella is not conspecific with some paratypes with a parallel-sided glabella (Lisogor, 1977). The present new species differs from all the species established on cranidia in having a notably narrower (sag.) preglabellar area, and from those except T. obsoleta in having larger and wider (tr.) palpebral lobes; however, T. obsoleta differs in its poorly developed glabellar furrows and evenly curved occipital furrow. There are two species established on pygidia, among which the new species is closely comparable in pygidial outline to T. conica from eastern Tienshan, Xinjiang (Zhang, 1981) but differs from the latter in lacking the interpleural furrows on the third segment and in bearing denser and stronger terrace lines. Occurrence Mid-upper part of Shenjiawan Formation (HF6), Upper Cambrian; Qiangongping, Fenghuang, western Hunan.