744 MR. C, TATE REGAN ON [Juiie 19, 



riidfe each radial consists usually of three segments, the proximal 

 being- longer than the middle ones. In the former family (text- 

 fig. 119, B, p. 743) the distal segments are short, in the latter 

 (text-fig. 119, A) they are more or less elongate. The Orectolohidfe 

 have a more specialised type of fin (text-fig. 119, C), which bears 

 considerable resemblance to that of the Squalidse. The pro- 

 pterygium is usually small or absent, and the mesopterygium is 

 enlarged and expanded distally ; it is more or less similar to the 

 metapterygium, from which it is almost completely separated by an 

 oval foramen, and bears about the same number of radials, each of 

 which is simple and formed of three or more segments. 



The mixopterygia (text-fig. 117, B, p. 739) have a very uniform 

 and special structure throughout the suborder. The axial cartilage 

 is dorso-ventrally flattened ; it is usuedly only partly separated from 

 the basipterygium by a single small proximal segment ; the acces- 

 sory cartilage is small, rounded, oval or oblong in shape. The 

 dorsal and ventral marginal cartilages are elongate and extend 

 to the proximal end of the axial cartilage ; their free edges are 

 approximated and, in the Scyliorhinidee, may even coalesce. The 

 terminal cartilages vary somewhat in number. The glandular sac 

 contains no special glandular body. 



Family 1. Odontaspidid^. 



No nictitating membrane ; no oro-nasal grooves ; last gill-cleft 

 in front of the base of pectoral*. Rostral cartilages convergent 

 anteriorly. Vertebral centra with secondary calcifications extending 

 from the central double cones to the periphery, leaving fou.r 

 principal uncalcified areas radiating to the bases of the neural and 

 hfemal arches. Pectoral fin with small propterygium and meso- 

 pterygium ; radials mostly attached to the metapterygium of 

 moderate length. 



The genera Odontasins and Scaj)anorhynchus, which comprise 

 this family, date from the Cretaceous. They may be distinguished 

 from the Lamnidpe by the subequal dorsal fins. I have examined 

 a centrum of Odontaspis, which presents exactly the same 

 appearance in transverse section as that of Orectolobus, described 

 by Hasse. 



Family 2. Lamnid^. 



Closely allied to the Odontaspididse, diflfering as follows : — Last 

 gill-opening, if small, vertically above the origin of the pectoral fin, 

 if wide extending downwards in front of the base of the pectoral. 

 Pectoral radials long, extending to the free edge of the fin. 



Large pelagic Sharks, with spiracles minute or absent, pectoral 

 fins falcate and caudal strongly heterocercal. The second dorsal 

 fin much smaller than the first and opposite to the anal. Most 

 of the existing genera appear to date from the Cretaceous. 



* In a stuffed specimen of Scapanorhynchiis owstoni the last gill-opening appears; 

 to be anterior to the pectoral fin. 



