460 



FISHES 



extinct genus Sdero7'hynchus from the Upper Chalk of Mount 

 Lebanon, in which the smaller size and more superficial position 

 of the rostral " teeth," and the absence of sockets in the rostral 

 cartilage, prove that the " teeth " approximate more to ordinary 

 dermal spines in this genus than in any of the more recent Saw- 

 Fishes. An extinct' genus Frojoristis, from the Upper Eocene of 

 Egypt, with non-socketed teeth, and species of the existing genus 

 Pristis from the English Middle Eocene, are also known. 



Fam. 2. Rhinobatidae. — Owing to the increased expansion 

 of the pectoral fins^ and the forward growth of their anterior 

 cutaneous portions along the sides of the head, as well as back- 

 wards along the trunk, the body now assumes a sub -rhombic 

 shape, and approximates to the disc of the more typical Batoidei, 



Fig. 263. — Rhinobatus granulatus. (From Miiller and Henle.) 



but the tail with its dorsal and caudal fins is still strongly 

 developed, and blends imperceptibly with the trunk in front. 

 Teeth very obtuse. No electric organs. About five genera and 

 twenty species are known, distributed in most tropical and sub- 

 tropical seas. 



The cosmopolitan Rldnolatus is represented by species from 

 the Mediterranean, the Eed Sea, the west coast of Africa, the 

 Indian Ocean, Australia and China, as well as from the Atlantic 

 and Pacific coasts of America, and the Galapagos. Rhyncliohatus 

 ranges from the Eed Sea through the Indian Ocean to China, 

 Zapteryx occurs at San Diego and Panama, and Platyrhinoidis 

 on the Californian coast. Trygonorhina is an Australian 

 genus. 



The family dates from the Upper Jurassic. Bhinolatus is. 



