250 FROM FISH TO PHILOSOPHER 



liorhinidae and Hemiscyllidae, which include the com- 

 mon western dogfishes, ScyUium canicula and S. catulus, 

 and the eastern ChUoscylliutn griseum and C. indicum. 

 The Greenland shark, Laefmzrgi/5 borealis (family Som- 

 nioscidae), is allegedly unique in producing eggs devoid 

 of a homy covering, which are deposited on the sea 

 bottom and fertilized externally (?I) {49, pp. 432 f, 



469 f; 69; 72, p. 96}. 



The only examples of viviparity among the bony fishes 

 occur in certain families of the Blenniidae {Zoarces)^ 

 the Cyprinodontidae (Gambusia, Anahleps), the Scor- 

 paenidae (Sefcosfe^), theComephroidae (Comephorus) , 

 and the Embiotocidae (Surf-fishes) . {49, p. 418.} 



It is of interest that a few teleosts are hermaphroditic 

 and self -fertilizing (Serranus cahrilla^ S. hepatus and 

 S. scriba and Chrysoprys auratus) , while hermaphrodit- 

 ism may occur as an occasional variation in the cod, 

 mackerel, and herring {49, p. 420}. 



According to MacFarlane {36}, the Permian Ctena- 

 canthii and the Triassic hybodont sharks were restricted 

 to fresh water, and it is not imtil the Jurassic that the 

 latter begin to appear in marine deposits. Consequently 

 he believed that aU elasmobranch evolution proceeded 

 in fresh water imtil Jurassic time. But it may be that the 

 Triassic forms, and indeed the ctenacanths and hybo- 

 donts that carried on through the Permian stricture, were 

 euryhaline, as are certain species vdthin the recent 

 genera Carcharhinus, Sphyrna, Mustelus, Squalus, 

 Pristis, Dasycptis, Raja, and others {69}. 



In respect to the phylogeny and habitat of the Paleo- 

 zoic elasmobranchs, we have followed Moy-Thomas 

 {66}, White {71, 72}, Romer and Grove {45}, and 

 Romer {42}. 



A list of recent fresh-water elasmobranchs is given by 

 Smith {69}. 



