恐鱼类的新材料

本文记述了采自云南盘溪的一恐鱼类的新材料,代表该类的一新种。这一化石的发现和记述,对于地层的对比和了解该类化石的地理分布均有一定意义。

NEW MATERIALS OF DINICHTHYIDAE

A new species of Dunkleosteus, D. yunnanensis sp. nov. is discribed in the present paper. The specimens occuring in association with the Panxiosteus ocullus and some plants, were collected from the bottom of Yidate Formation, probably upper Middle Devonian of Panxi in Huaning county, Yunnan Province. The new species is characterized by the size obviously smaller than Dunkleosteus terrelli and by rare tubereles on the dermal bone at the centre. The nuchal plate is rather short with a small process at the post-margin and triagular in shape. The posterior margin of the cranial roof is moderately emarginate, the ventral surface of the nuchal near the posterior margin has a massive nuchal thickening. The suborbital is very large, the blade of the suborbital is very long and the submarginal was thickened,it is nearly three times the size of handle. The handle of suborbital is shorter and smoth outside. It is composed of two parts, one, the real handle, is formed of the immediate prolongation of the blade, the other part of handle is about tongue-shaped and is placed lower down. It beging nearly at the base of the handle. The inside of the handle with two ridges from the upper front corner of the blade bebins a ridge (R_1) which runs downward and then it curves its greatest hight about the curving point. R_2 is not clear but juding from the part that was preserved it is low too, but wider. The infraorbital sensory canal runs from the upper front corner of the blade downward nearly parelled to its margin. Not far from the lower margin of the suborbital, this canal curves sharply forward at an angle of nearly 120° from its originial direction and continues onto the handle, there it gradually approaches the lower margin, and at last crosses it into the tongue-shaped part. The supramaxillary sensory canal runs parallel with the lower margin of the suborbital, beging at its lower hind cirner. A little before, it meets the above mentional canal, it curvey sharply upward and fuses with the infraorbital sensory canal. The antero-dorso-lateral plate is very incomplete. Juding from the preserved part, it may be large and slightly carved. The condyle, serving as an attachment between body and head, is placed nearly in the middle of its front margin. The condyle is himespherical in shape. The median part of this plate is quite plane. The main lateral line canal runs from the condyle nearly horizontally to the hind of the plate, another canal is very short and about a third of the above one. Remarks These materials are very similar to the Dunkleosteus terrelli in the form and structure Of the nuchal plate and the suborbital plate, but the new materials differ from the D. terrelli in two points. Firstly, the nuchal plate and the suborbital plate with ornamention on its centre. Secondly, the levator pit long, but no ridge in it. Thus the new materials dealt with in paper are named by the author as a new species Dunkleosteus yunnanensis sp. nov.