BY WILLIAM A. HASWELL. M.A., B.SC. 89 



of the vertebrae, and two lateral ones continuous with the transverse 

 processes. Its upper surface slopes obliquely upwards and 

 forwards to the parietal groove, which is a deep pit continued 

 forwards for a short distance by a rapidly shallowing concavity. 

 The elevations for the anterior and posterior semi-circular canals 

 are well marked and "prominent. The articular surface for the 

 hyo-mandibular is simple and not raised from the general surface 

 The orbit is bounded behind by a very prominent post-orbital 

 process with which the palato-quadrate articulates. There is no 

 basal plate ; in front of and below the orbit and projecting down- 

 wards and outwards, is a prominent pointed process, the extremity 

 of which is free ; this, according to Gegenbaur, corresponds to 

 the ant-orbital cartilage in Rays ; it is not, however, related to 

 the wall of the nasal capsule, but is placed behind the latter and 

 arises from the contiguous portion of the base of the skull. The 

 rostrum is represented by a pair of short processes of the ethmoidal 

 region not extending beyond the level of the nasal cartilage. The 

 walls of the nasal capsule are formed of cartilage only behind 

 internally, and above, with a short external rim. The nasal 

 cartilage is ring-shaped, with two short horas directed down- 

 wards. Below the orbit there is, as in Hexanchus griseus and 

 Heptanchus cinereus, an extensive vertical articular surface for 

 the palato-quadrate. 



The hyo-mandibular is a long, narrow, curved and flattened 

 cartilage bearing the hyoid at its distal extremity, and suspending 

 also the palato-quadrate, though chiefly related to the hyoid. The 

 hyoid cornua are very large : they bear a few delicate rays ; 

 distally they articulate with the hyoid copula. The first branchial 

 arch has no copulare ; its venti'al mesial cartilage is connected with 

 the postero-external angles of the hyoid copula The following five 

 arches have all well- developed copularia ; the second and third 

 have distinct though small copulae ; the fourth has no separate 

 copula, the latter having become fused with the left copulare. The 

 fifth and sixth copularia unite with the basibranchial plate. The 

 seventh arch has no copulare as well as no basal, its ventral is 

 broad and flattened, and unites with the basibranchial plate. The 



