410 MESSRS. HANCOCK AND ATTHEY 



towards the margins in many places considerable patches of 

 them lie in their natural order, particularly on the right thoracic 

 expansion, on a large portion of which the shagreen is entire. 

 The tubercles are very minute, requiring a powerful lens to ex- 

 hibit them, and the lower powers of the microscope to display 

 their characters. They are many sided, irregularly formed bodies, 

 closely fitting together like mosaic work ; the surface is a little 

 raised and beset with irregular ruga?. This is the appearance 

 presented where the shagreen is undisturbed ; but it is doubtful 

 whether it may not be the under surface that is presented to 

 view. In places where the tubercles are scattered numerous 

 shining bodies are observed ; these are about the same size as 

 the tubercles, and, like them, are irregular in form, but are more 

 gibbose, and have a ridge or two on the surface, which are pro- 

 duced into points at one of the sides. From analogy we might 

 suppose that these bodies exhibit the upper surface of the shag- 

 reen-tubercles ; but further observations are required to deter- 

 mine this point. 



The teeth are boss-like in form, somewhat elongated and ridged 

 or carinated along the longer axis ; the sides are considerably 

 expanded in the centre, the expansions dying out towards the 

 ends of the tooth : usually the expansion is more produced on 

 one side than on the other, and the ridge inclined to the opposite 

 side. The expansions are frequently transversely ridged or 

 plaited, and sometimes tuberculated. The central ridge or ca- 

 rina of the crown is arched in the long axis of the tooth, follow- 

 ing the curvature of the surface, and is frequently reduced, as 

 if by wear. The whole surface of the tooth, as well as the la- 

 teral expansions, is covered with a thick brownish- white enamel, 

 and is coarsely punctate, the punctations being most conspicuous 

 when the enamel is worn off. The tooth measures two-tenths 

 of an inch in length : a variety, however, four or five of which 

 have occurred at Kenton, is twice that size ; but it is more ob- 

 lique than the small form, has no coronal carina, and is broad 

 and rounded on the upper surface ; in all other respects it agrees 

 with the small and usual form. It is quite possible that these 

 large teeth may belong to another species. 



