62 MESSRS. HANCOCK AND ATTIIEY ON r 



a little convex ; the surface is slightly convex, and is furnished 

 with twelve or thirteen deep, sharp, parallel, approximate ridges, 

 which are strongly tuberculated towards the outer margin, and 

 divided by narrow, deep, angulated grooves ; they are arched 

 posteriorly, and enlarged towards the exterior border, but do not 

 at all assume a radial arrangement ; the anterior ridge, which is 

 wider than the others, is reflected and prolonged for some dis- 

 tance beyond the outer margin ; the tubercles are conical, with 

 obtuse points ; those next the external border are coated with 

 shining enamel, and are well produced. 



The mandibular tooth difi'ers from the palatal in being nar- 

 rower, and is so convex as to resemble the longitudinal section 

 of a cylinder ; the two or three anterior ridges, too, are much 

 shorter than the rest, the inner margin sloping rather rapidly 

 away in front. 



There are half-a-dozen of this species in our collection, all of 

 which were obtained at Newsham ; and in the Newcastle Mu- 

 seum there are two others, which were likewise procured from 

 the same locality, and are from the collection of G. B. Forster, 

 Esq. They are all in excellent condition, agree perfectly well in 

 every respect, and can be at once distinguished from C. cristatus 

 by the deep and sharp ridges and by the form of the tubercles, 

 which in C. tuherculatus are always exactly conical (when they 

 are in a fresh state) at the outer margin. When worn, how- 

 ever, they are flattened at the sides in the direction of the ridges ; 

 and then they are wedge-shaped, and they and the whole of the 

 ridges become granulated. 



3. Ctenodus corrugatus, n. sp. 



Tooth plate-like, thin, subtriangular, three inches long, two 

 inches broad ; the surface is slightly convex, and raised into nine 

 stout somewhat irregular rounded ridges or wrinkles, the grooves 

 dividing them being wide and rounded ; the ridges die out to- 

 wards the inner and outer margins, but are enlarged a little as 

 they approach the external border, and are indistinctly and irre- 

 gularly tuberculated ; the inner margin is nearly straight, the 



