44 MR. A. D. IMMS ON I'HE DENTICLES [Jan. 1 7, 



pavement of denticles very closely packed together. A similar 

 investment covered the branchial arches up to the bases of the 

 gill-filaments. The specimen examined measured 56 cm. in length. 



4. MuSTELUS L^vis Rond. — In an example measuring 150 cm. 

 long the distribution of denticles over the mouth and pharynx 

 was similar to that in S'phyrna. It will be seen on refeiiing 

 to PI. III. fig. 1, that the denticles of this species are rhomboidal 

 in shape with rounded angles, a,nd each has a well-defined basal 

 plate. They are very closely packed together, so that each partially 

 overlaps two or more of its fellows immediately behind. Their 

 basal plates are also seen to closely inter digitate with one another. 



5. Galeus (Galeorhinus) canis Rond. — Denticles in this 

 species have a distribution identical with that found in Sphyrna 

 and Mustelas. In PL III. fig. 2 is represented a strip of the 

 mucous membrane of the pharynx with the denticles in situ. It 

 will be observed that they are closely and regularly ai-ranged 

 together, but no imbrication takes place as in Mustelus. The fish 

 examined measured 155 cm. in leng-th. 



Fam. Lamxid^. 



6. Lamna (Oxyrhina) cornubica Gmelin. — In a specimen 

 measuring 79 cm. in length the denticles had a distribution 

 identical with that found in the three preceding genera. 



Fam. NoTiDANiD^. 



7. NoTiDANUs (Heptanchus) cinereus Gmelin. — In an example 

 of this species measuring 65 cm. in length denticles were found to 

 be generally distributed over the lining of the mouth and pharynx, 

 and also to extend over the pharyngeal edges of the branchial 

 ai'ches. They were absent, however, from the anterior and 

 posterior faces of the latter. In form they are characteristically 

 tricuspid, as is represented in PI. III. fig. 3, and are identical 

 in all i-espects with the placoid scales of the skin. 



Fam. ScYLLiiD^. 



8. ScYLLiUM CANICULA L. — After an examination of a number 

 of examples of this fish, which were used for class demonstrations, 

 no denticles were to be detected over any part of the lining of 

 the mouth or pharynx. 



9. OniLOSCYLLiUM INDICUM Gmelin. — In a specimen 34 cm. long 

 denticles were found scattered somewhat irregularly over the 

 lining of the mouth and jjharynx, but they did not extend on to 

 the branchial arches. 



10. Pristiurus melanostomus (Rafinesque) Blainv. — In a very 

 young individual, 14 cm. in length, oral and pharyngeal denticles 



