滇东中泥盆统的节甲鱼类化石

本文记述了节甲鱼类中称为北极鱼类的三个新属种:Exutaspis megista,Kunmingolepislucaowanensis,Yangaspis jinningensis,化石分别采自武定海口组(广义),海口和晋宁的海口组。代表我国中泥盆世该类化石鱼类的首次记述。

ON THREE NEW ARTHRODIRES FROM MIDDLE DEVONIAN OF YUNNAN

The arthrodires described here were collected from Middle Devonian Haikou Formation, which is widely distributed in Yunnan and well known for plenty of Bothriolepis and yielded petalichthyids Quasipetalichthys haikounensis, crossopterygian and non-Bothriolepis antiarchian remains as well as plants. Kunmingolepis lucaowanensis gen. et sp. nov. and Yangaspis jinningensis gen. et sp. nov. came from the districts of Kunming and Jinning respectively. In Kunming and its neighboring regions including Jinning Haikou Formation (S. S) overlies pre-Devonian rocks and is directly succeeded by Upper Devonian rocks, Zaige Dolomite. It ranges in thickness from several to about 30 m. But in Wuding district, where Exutaspis megista gen. et sp. nov. came, Haikou Formation lies on Upper Lower Devonian Pochiao Formation and is over 350 m in thickness. There the bed carrying Exutaspis together with antiarchian Wudinolepis woni is about 30 m under Bothriolepis bed and 27 m above Pochiao Formation.Exutaspis megista, the largest phlyctaeniidae fish known so far, is reprented by a model of ventral face of the head roof. It is 21 cm in length from anterior margin to posterior end of the head roof and 22.5 cm in breadth between posterolateral angles. The head roof is remarkable in having gently concave anterior margin, a pair of prominent posterolateral and less distinct postero-masial angles, a very strong convex posterior end. The anterior margin of the head roof extends forward beyong the anterior border of the dorsal wall of the postethmo-occipital bone and laterally to form the anterior boundary of the orbital notch. Thus, it is probably that the postnasal plate is fused with the preorbital one and the lost rostral capsule may be rather reduced. The orbital notch is very deep. The sclerotic rim has left the print together with a few bone remains of it in original position. The well developed anticular fossa has an oval shape and rough surface. The para-articular projects as processes lateral to both sides of the head roof.On the sensory canal system only twe piece of the supraorbital canal have left their impressions. It seems that the supraorbital canals run backward not far from the anterior margin of the head roof. The ornamentation consists of small round tubercles.The structure of the ventral face of the head roof are well shown in the model. The latero-caudal descending lamina is poorly developed, only the part anterior to the anterior post-orbital process can be seen. The supraorbital area is fairly distinct, On both sides of the model of head shield lateral to the dorsal wall of the endocranium there is a very deep groove, which just forms the anterior boundary of the (?)ucullaris depression and the postorbital process liens on its bottom. The same structure was also exhibited in Kujdanowiaspis (Stensio 1945, fig. 1) and Sz(?)lepis (Liu 1979, p1. I. 1). In fact, this groove should be caused by a ridge for which the name cucullaris ridge is proposed here. It descends from the ventral face of the head roof. The cucullaris depression is very remarkable, stretching just from cucullaris ridge backward to the median thickening. Along the posterior margin the ventral surface of the head shield thickens into a strong median thickening, which projects laterally to form a para-articular and is pitted with the articular fossa median to the para-articular process. The endolymphatic thickening extends backward and somewhat laterally, and finally joins the median thickening just in front of the articular fossa.Except that the subnasal shelf is unknown, the postethemo-occipital bone is essentially the same as those in Kujdanowiaspis, Stuetzeaspis and Szelepis. But it has rather short otic region with remarkable anterior postorbital process which extends postro-Iaterally as far as the margin of the head roof. The posterior postorbital process is slender and does not bifurcate in distal end. The occipital region is narrow but with developed supravagal process.Yangaspis is represented by an anterior ventro-(?)ateral plate with stout but damaged spinal plate. The anterior ventro-lateral plate is much broad and its anterior margin and internal overlap areas suggests that in this animal no independ antero-ventral plate has developed. In the proportion of the breadth to the length the anterior ventrolateral recalls that of petalichthyids Lunaspis, but in Lunaspis this plate has a straight median margin and is contact with the opposite one in middle part. Under our poor knowledge of the trunk armour of petalichthyids, we would like to put Yangaspis into Phlyctaeniidae.The Kunmingol(?)pis is represented by five anterior lateral plates. The plate is roughly trapezoid in shape. It is gently convex with highest point near the centre of the plate and divided into quadrants by ridges. The anterior quadrant is slightly inturned but not forms a clearly defined apron. The ornamentation consists of small tubercles. Comparing with well-known forms of "Arctolepids" the anterior lateral plate much more approaches the corresponding ones of "Kujdanowiaspis" (White 1969, figs. 23—28), but it differs from all in having longer basal margin, backwardly sloping dorsal margin, a deep emargination for intero-lateral plate in lower part of the anterior margin and a large emarginate posterior margin unoverlapping posterior lateral plate.