1906.] SELACHIAN FISHES. 745- 



Family 3. Orectolobid^. 



Allied to the Odontaspididse, but distinguished by several 

 features of specialisation. Oro-nasal grooves present; last two to- 

 four gill-openings above the base of the pectoral. Rostral carti- 

 lages, if present, short and not convergent. Pectoral meso- 

 pterygium enlarged and expanded distally, more or less similar to 

 the metapterygium ; an oval foramen between the mesopterj'gium 

 and metapterygium. 



Examination of a stuffed Sjoecimen of the large Rhinodon 

 typicus leaves no doubt that it is closely related to Ginglymostoina,. 

 from which genus it differs only in those features in which it. 

 resembles the Basking Shark, Cetorhinus maximus, i. e. the small 

 teeth, long gill-rakers, wide gill- clefts, &c., which are obviously 

 of physiological rather than phylogenetic importance. 



Probably the Mesozoic Palceoscyllium and Cantioscyllmm should 

 be placed in this family, all the members of which have the dorsal 

 fins placed posteriorly, the first not or scarcely in advance of the 

 ventrals. 



Family 4. Scyliokhinid^. 



No nictitating membrane ; no oro-nasal grooves; last one or two 

 gill-clefts above the base of the pectoral. Rostral cartilages 

 convergent anteriorly. Vertebral centra with secondary calcifi- 

 cations as in the preceding families or variously degenerated ; 

 when complete, with four short calcified rays extending from the 

 central double cones into each of the principal uncalcified areas. 

 Pectoral fin with small propterygium and mesopterygium ; radials 

 of moderate length, mostly attached to the metapteiygium, of 3 

 segments. Mixopterygia with the edges of the marginal carti- 

 lages united, forming a tube. 



Scyliorhinus and Fristiurus comprise Dog-fishes of small or 

 moderate size, either littoral or inhabitants of the deep sea. 

 The latter appears to date from the Jurassic, the former from the 

 Cretaceous. The spiracles are well-developed, the first dorsal i& 

 above or behind the ventrals, and the caudal is very feebly 

 heterocercal. 



I have examined a spirit-specimen of the rare Psendotriacis 

 onicrodon, which agrees with Fristmrus in general form, in the 

 shape and position of the mouth, structure and position of the 

 nostrils and spiracles, in the presence of a fold of skin below the 

 horizontally elongated eye, in the position of the last gill-cleft and 

 the shajDe of the caiidal and paired fins. I have examined one of the 

 caudal vertebrae, in which, as in Fr-istiurus, the secondary calcifi- 

 cation is reduced to a thin peripheral layer. From other 

 Scylioi-hinidse, Fseudofriacis is distinguished by the longer and 

 more anteriorly placed dorsal fin. 



The Cretaceous and Eocene Mesiteia may belong to this famil}''. 



