VEETEBEATES. 125 



The foregoing diagnosis of the characteristics pertaining to each 

 of the several dental elements here recognized as having formed 

 part of the dentition of this interesting species, presents in suffi- 

 cient detail the peculiarities which distinguish it in comparison 

 with other species of the genus. It remains briefly to observe the 

 association of certain teeth in their original relative position upon 

 the jaws, examples of which, fortunately, have been obtained by Mr. 

 Van Home and Prof. Worthen. The most complete specimen of 

 the mandible shows the posterior and median teeth planted upon a 

 thin semi-osseous tissue composed of coarse granules of ossific mat- 

 ter, the walls of which are strengthened from within 'by a system 

 of transverse bars, like girders, which serve to maintain the shape 

 of the surface upon which the crushing plates rest. The teeth are 

 separated from the supporting rami by a film of calcite, which 

 probably represents the bulk of the tegumentary or formative tissue 

 that enveloped the dentigerous portions of the jaw. The mandible 

 extends anteriorly into a slightly produced, bluntly rounded extrem- 

 ity, which from the inferior surface shows on either side of the 

 symphysial line a shallow pit, which may indicate the position of 

 the corresponding concavity of the dental plate or tooth occupying 

 the extremity of the jaw; but not a vestige of the latter exist in 

 the specimen, and therefore in regard to their form we are as much 

 in the dark as heretofore. Although the maxillary anterior teeth 

 have been provisionally identified, we are unable to conjecture even 

 the form of the opposed mandibular teeth whether they presented 

 a series of distinct coronal crests or merely a simple inrolled plate. 

 A remarkable specimen of the mandible, belonging to the Wood- 

 wardian Museum, obtained from the mountain limestone of Bristol, 

 England, and which was described by Professor Owen, (Geol. Mag. 

 1867, IV, p. 59, PI. Ill, f. 1, 2,) shows the extremity of the rami of 

 Cochliodus contortus, Agass., occupied by a third tooth, the smallest 

 of the series, and presenting a triangular shaped, inrolled plate, 

 traversed by a prominent median ridge which is described as being 

 "very convex and obliquely and gently contorted from behind and 

 below, upward, inward and forward, with a slight increase of breadth 

 or fore and aft diameter. * * * The anterior lobe seems to have 

 had the form of a small tubercle, but its summit is broken off ; the 

 posterior lobe is a narrow', seam-like, raised border, extending fur- 

 ther back on the outer side, fig. 2 a, than on the inner side of the 

 ranius." Our specimens, unfortunately, afford no means of confirm- 

 ing the observations based on the Bristol specimen, nor do the col- 



