46 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [BuU. 



ganoids in the development of a paired series of transversely 

 elongated branchiostegal rays to replace the pair of jugular plates 

 between the mandibular rami; infraclavicular plates, however, 

 are retained in both groups. Nearly all thq older forms have a well 

 developed rhombic and ganoid squamation. So far as known, 

 the chondrocranium is but little ossified, and the cranial bones 

 are mainly dermal. 



The evolutionary history of the sturgeon tribe is thus sum- 

 marized by Professor Bridge in the Cambridge Natural History 

 volume on Fishes (1904, p. 485) : 



" The Chondrostei are first represented in the Lower Devonian 

 by the solitary Palaeoniscid genus Cheirolepis, a contemporary of 

 the earliest Crossopterygii. They occur throughout the Mesozoic 

 period, except in the Cretaceous, and also in the Eocene, and, 

 while steadily diminishing in number and variety, they gradually 

 approximate to their degenerate and in some respects highly 

 specialized descendants, the sturgeons and paddlefishes of the 

 existing fish fauna. Of the seven families included in the group, 

 the Palasoniscidse are the oldest and most generalized. The 

 Platysomatidae are a specialized offshoot from the Palasoniscidse, 

 and, if they are rightly to be considered as Chondrostei, perhaps 

 the same may be said of the problematic Belonorhynchidas. On 

 the other hand, there are certain features which indicate an ap- 

 proach to Fishes of an altogether more modern type. Finally, 

 the Chondrostei represent a stage in a career of degeneration, the 

 climax of which is reached by the modern Polyodontidse and 

 Acipenseridse." 



Family CATOPTERID^. 



Trunk elongate or elongate-fusiform; tail abbreviate-hetero- 

 cercal. Head bones well developed, ganoid; no median series 

 of cranial roof-bones ; teeth slender, conical ; eye far forward, 

 and snout prominent; mandibular suspensorium more or less 

 obliquely directed backward and downward. A series of branchi- 

 ostegal rays present. E>orsal fin single and not much extended. 

 Scales rhombic, ganoid. 



This short-lived family, in which are comprised not more 

 than three closely related genera {Catopterus, Perleidus, and 

 Dictyopyge), appears in the early Mesozoic just as the large and 

 successful group of Palaeoniscid fishes are entering upon their 



