114 STUDIES ON THE ELASMOBRANCH SKELETON, 



Selachoidei, and the olfactory capsules are remote from the orbits. 

 The hyo-mandibular takes a comparatively unimportant part in the 

 suspension of the lower jaw and palato-quadrate. 



There are two dorsal fins, and these possess broad plate-like 

 cartilages, and are closely related to the spinal column. 



LAMNID.E. 



The centra of the vertebrae present radiating lamellae. 



The articular surface for the hyo-mandibular is simple, but 

 borne on a projecting portion of the postero lateral region of 

 the skull. The post-orbital process does not articulate with 

 the palato-quadrate. The orbit has a cartilaginous floor. There 

 is no ant-orbital process representing the ant-orbital cartilage 

 of the Rays. The external branchial arches are well-developed. 

 There is a well developed three-rayed rostrum. The hyo-mandibular 

 bears a series of cartilaginous rays. The hyoid copula is a broad 

 plate. The meso- and metapterygia are partly coalescent ; the 

 primary rays of the pectoral fins have intercalated among them a 

 series of accessory rays which do not reach the basal cartilages. 

 The dorsal and anal fins possess no broad basal cartilages and do 

 wot articulate with the spinal column. 



ScylliolamnidjE. 



The centra of the vertebrae present radiating lainellse. 

 The articular surface for the hyo-mandibular is a deep conical 

 hollow into which fits a peg-like process of the latter cartilage. 

 The rostrum is single, and does not advance much beyond the level 

 of the olfactory capsules. There is a basal plate forming a floor 

 for the orbit. There is neither ethmoidal canal nor notch. 

 There are rays on the hyo-mandibular as well as on the hyoid arch. 

 The hyoid copula is a broad plate. The external branchial arches 

 are rudimentary. The pectoral arch presents no ventral mesial 

 flexible interval as in other Sharks. All the three basal cartilages 

 of the pectoral fin are well-developed. The unpaired fins do not 

 present expanded basal plates. 



