32 



NATURAL SCIENCE. 



no pectoral or pelvic fin hitherto described retains the arrangement. 

 The well-known paddle of Ceratodus and of the Pleuracanth Sharks 

 (Fig. 7), with its median axis and double series of divergent branches, 

 has hitherto been the nearest approach to the primitive type ; and 

 this was at first regarded as the " archipterygium " by Gegenbaur. 

 Within the last few years, however, several specimens of a peculiar 

 elongated Elasmobranch, with C/^^o^z/s-shaped teeth, have been dis- 

 covered in the Cleveland shale at the base of the Carboniferous 

 Formation in Ohio, U.S. A. 3; and, in the opinion of the present writer, 

 the pectoral fin of this shark at last reveals one of the least-modified 





''^^mm 



w^ 



"""Mill 





Fig. 5. 



Fig. 6. 



Fig. 5. — Pectoral fin of " CladocUn " fylcri, from the Lower Carboniferous of Ohio. r. Complete 

 rays ; ic. Intercalated remnants of rays. Right border preaxial. From a specimen 

 presented to the Britisli Museum by Dr. J. S. Newberry. 



Fig. 6. — Pectoral fin oi. Eusthcnopteron foordi, from the Upper Devonian of Canada, b. Basal 

 cartilage of fin. Right border preaxial. Specimen in British Museum. 



conditions of the endoskeleton of the lateral fin-fold that can be 

 expected in a fish in which this fold is already sub-divided into its 

 ordinary two remnants. No fused basals can be detected with cer- 

 tainty in any of the specimens the writer has examined ; and, as 

 shown in the fin represented in Fig. 5, none of the parallel car- 

 tilaginous rods that support the fin-membrane are transversely 

 jointed. The most singular feature of the fin consists in the evidence 

 it affords of that crowding and concentration we have already 



■^ See photographs by J. S. Newberry, in Monogr. U.S. Geol. Survey, No. xvi. 

 pis. xHv.-xlvi. 



