50 



PISCES. 



are only cyclospondylic. Here, however, may probably be 

 placed the Spinacidae, which are of little palseontological 

 interest and are not known to date back further than the 

 Upper Cretaceous. It is quite possible also that the Palaeozoic 

 Petalodontidae and Psammodontidae, as yet known only by 

 the imperfect dentition, may prove to be early types of the 



FIG. 39. 



Squatina speciosa; two-thirds nat. size. U. Jurassic (Lithographic Stone) ; 

 Bavaria, a, mandible ; b, pectoral arch ; c, pectoral fin ; d, pelvic arch ; 

 e, pelvic fin. (British Museum, no. 37013.) 



same sub- order. The Lower Carboniferous teeth named Psam- 

 modus most nearly resemble in general aspect the grinding 

 teeth of the existing Myliobatida?. 



The Squatinidae (or Rhinidae ) are represented by the typi- 

 cal genus Squatina in the Lithographic Stone (Upper Jurassic) 



