90 PISCES. 



jaws consists of a series of large, enamel-tipped, conical teeth, well spaced, 

 with minute intermediate teeth ; and some of the inner bones of the 

 mouth are also provided with minute teeth. A small operculum is 

 attached by an articulation near the upper end of its anterior border to 

 the hyomandibular ; but there is no evidence of any other ossification 

 either in the opercular or branchiostegal membrane. The notochord is 

 shown to have been persistent, and there are no undoubted ossifications 

 in the notochordal sheath. The neural and hsemal arches, however, are 

 much expanded, the former united by zygapophyses and bearing short 

 delicate spines, the latter in the caudal region symmetrical with the 

 neurals. Long slender ribs have also been observed in some specimens. 

 The paired fins are small, apparently exhibiting a very feeble lobation, and 

 consisting of delicate rays. The clavicle is also small and sickle-shaped, 

 with a triangular plate affixed to its postero-inferior border ; the pelvic 

 fin-supports are unknown. The dorsal and anal fins exhibit a single series 

 of robust supports much less numerous than the dermal rays ; the base 

 of the caudal firi is unknown. There are no fin-fulcra. A median 

 longitudinal series of scutes extends along the dorsal and the ventral 

 border ; while another series supports the canal of the lateral line on each 

 side. The typical species, B. striolatus, is a small fish from the Upper 

 Keuper of Raibl, Carinthia ; but species from the Keuper of Lombardy 

 and the supposed Triassic of New South Wales probably attained a length 

 of half a metre. Detached skulls from the Lower Lias of Lyme Regis and 

 the Upper Lias of Wiirtemberg (B. acutus) afford most information 

 concerning cranial osteology. 



The Triassic and Rhsetic teeth and fragments of jaws 

 named Saurichthys belong either to Belonorhynchus or to a 

 closely related fish. 



It may perhaps be doubted whether the Belonorhynchidse 

 are correctly associated with the Palseoniscids and Acipenseroids, 

 but the relationships of the Liassic family of Chondrosteidae 

 seem to be quite indisputable. These fishes agree with modern 

 Acipenseroids in most essential characters ; but they differ 

 (i.) in the arrangement of the elements of the cranial shield 

 and (ii.) in the presence of a suboperculum and a well-developed 

 series of branchiostegal rays. In the two latter particulars they 

 approach the Palseoniscids, and it is significant that they do not 

 appear until this family has become of subordinate importance. 

 So far as known, they are exclusively confined to the English 

 Lias, and thus far only one genus has been discovered sufficiently 

 well preserved for detailed description. 



