238 



M. 



Depth of the dentary at the first tooth 0.080 



Length of the dentary to the first tooth 0. 020 



Length of the first tooth 0.032 



Interval between the maxillary teeth 0.008 



Niobrara epoch of Phillips County, Kansas; discovered by Prof. B. F. 



Mudge. 



ENCHODUS, Agassiz. 



'o^ 



The massive premaxillary bones of this genus are well known. They 

 support an elongate fang at tlie anterior extremity. The maxillaries underlap 

 them, and support some elongate teeth near their anterior end. The anterior 

 denlaries are also longer than the others. The teeth are all anchyloscd by 

 expanded bases ; the posterior ones on an oblique alveolar surface. The long 

 teeth are removed by an absorption set on foot at the posterior basis of each, 

 which progresses until the crown readily breaks away. The successional 

 teeth appear in front of the old ones, appearing successively as the aiiimal 

 increases in size, so that the scars of those of preceding stages are only indi- 

 cated by successive curved lines, becoming more prominent from the back to 

 the front of the bone. 



_ The posterior part of the cranium of E. petrosus exhibits a supraoccip- 

 ital crest with short basis ; tliis element separates lateral pieces, which are 

 epiotic or |)arietal. They are separated by a concavity from the bone that 

 occupies the external posterior angle, which is epi- or opisthotic. On the 

 inferior view, no muscular tube appears, nor any otic foramen, such as exists 

 in the Saurodontidcc. The visible surfaces of the exoccipital, the pterotic, 

 the postfrontal and prootic, are subequal, and the alisphenoid is well devel- 

 oped. A strong rounded ridge extends from the postfrontal angle to the 

 anterior base of the prootic, which bounds a deep fossa which occupies the 

 point of union of the postfrontal, pterotic, and prootic Cervical vertebras are 

 not coossified nor modified in any especial manner. Their centra are rough- 

 ened with raised inosculating ridges. 



This genus has long been known from the Cretaceous of Holland and 

 England ; two or three species liave left their remains in the greensand of 

 New Jersey, and others occur in the chalk of Kansas. Dr. Leidy described 

 a species' from the Cretaceous formations of the Upper Missouri region, which 

 he called E shumardii. Several premaxillaries of a rather larger species were 



' Enchodua shumardii, Leidy, Proceedings of the Academy of Natural Sciences of Philadelphia, 1856, 

 p. SI")?, i.s a smaller species than any of those here described. 



