48 EXPLANATION OF PLATES 27^28. 



has brought clusters of these tubercles into contact 

 with the bone in several parts of fig. 1. (Original.) 

 Fig. 5. Magnified view of similar minute tooth-like tu- 

 bercles of Enamel, forming the Shagreen on the 

 skin of the head of the recent Squatina angelus. 

 See V. I. p. 269, Note. (Original.) 



Plate 27^ V. I. pp. 286 & 289. 



Beautiful cluster of palatal teeth of Ptychodus poly- 

 gyrus, from the Chalk. Insulated teeth of many species 

 of this Genus abound throughout the Chalk formation. 

 The mouth of these and all the other numerous extinct 

 species of Sharks in the family of Cestracionts, was lined 

 with a pavement of similar powerful teeth, forming a most 

 efficient apparatus, for crushing the shells of Crustacea 

 and Conchifera, which probably formed their principal food. 

 The surfaces of the Enamel are often worn away, like that 

 at PI. 27^ fig. 3. The strength and efficacy of these teeth, 

 viewed as Instruments for crushing shells, is very remark- 

 able. Beneath the Enamel, the body of each tooth is 

 composed of a strong mass of bone. (Miss F. C. Burgeon. 

 Original.) 



Plate 28. V. I. p. 303. 



Fig. 1. Represents the common calmar or squid (Loligo 

 vulgaris. Lam. Sepia loligo, Linn.) shewing the 

 place and excretory duct of its Ink bag, and the 

 position of the feet on the anterior margin of the 

 head. (Blainville.) 



Fig. 2. Side view of the Pen of the Loligo vulgaris, 

 shewing its position in the back of the animal, 

 fig. L (Original.) 



Fig. 3. Concave under surface of the same pen. (Ori- 

 ginal.) 



