i6 



CONNECTICUT GEOL. AND NAT. HIST. SURVEY. 



[Bull. 



latter part of that system by creatures which surpass them in 

 grade, and are perfectly recognizable as true fishes, possessing 

 as they do ordinary jaws and two pairs of lateral fins. These 

 oldest remains of typical fishes — they are called Acanthodians 

 after the name of the first described genus — are probably to be 

 regarded as Elasmobranchs, and evidently have not diverged very 

 far from the primordial stock which gave rise not only to the 

 line of sharks and rays, but also to different grades of higher 

 fishes. Acanthodians (Fig. 2) are a long-lived race, continuing 

 throughout the Paleozoic. An allied primitive tribe that was 

 less successful, and by reason of its long-bodied form is regarded 

 by some writers (Woodward) as senile, is that typified by 

 Cladoselache (Fig. 3), which is known from the late Devonian. 



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-■ ^-..■^■■•-..^v ■ ■'- —^ 



Fig. 3. Cladoselache fyleri Newberry. Cleveland shale 

 (Upper Devonian) ; near Cleveland, Ohio. Right lateral aspect, 

 about one-tenth natural size. A primitive shark, illustrating the 

 simplest kind of paddle-fins, which are supported by nearly par- 

 allel bars of cartilage (after Bashford Dean). 



During the Devonian appeared two large groups of fishes 

 with paddle-shaped fins. These groups are commonly known as 

 Lung-fishes and " fringe-finned " Ganoids — Dipnoi and Cross- 

 opterygii they are technically called. Their geological history 

 is peculiar. Both groups early acquired dominance, spread over 

 all regions of the globe, and seem indeed to have culminated in 

 the Devonian, being numerically and specifically more abundant 

 during that period than at any subsequent epoch. Only two 

 modern survivors of Crossopterygii are known from African 

 rivers (Polypterns and Calamoichthys). Of the long and archaic 

 line of Lung-fishes represented by Dipterus (Fig. 4) and its 

 associates in the Devonian, only the most generalized Ceratodont 

 type, represented nowadays by but three fresh-water genera, has 

 been able to persist until our own time. That the Ceratodont 

 type has had a continuous existence since the early Paleozoic 

 follows as a logical necessity from regarding the Dipterine group 



