11 



The superior surface of the skull is only partly preserved in one speci- 

 men. This renders it probable that there is a crotaphite foramen as in the 

 crocodiles, etc. The surfaces of the external cranial elements are finely 

 pitted, or rather punctured. 



Measurements. M. 



Total length of skull 180 



Width of skull at quadrates. .145 



" " " origin of zygoma 115 



" '•' " incisive foramen .056 



Length of dental series to posterior extremity of incisive 

 foramen, on curve .090 



Diameters of third molar from behind i anteroposterior . .010 



( transverse » .021 



Depth of mandible at fifth molar from behind 048 



Maxillary series of seven, and parts of the mandibular series of four, indi- 

 viduals, are in my collection. 



HELODECTES Cope. Genus novum. 



Maxillary bones of two species, which I refer to this genus, were found as- 

 sociated with many bones of appropriate size, among which are vertebrae of 

 the type of Empedodes. The characters observable are generally similar 

 to those of the Diadectidce, where I accordingly place the genus. Its 

 principal characters, the presence of two rows of teeth in the jaws, has 

 already been pointed out. I may add that there is apparently a large tooth 

 in the position of anterior incisor, in the typical species. 



The species differ in the arrangement of their teeth, as follows : 



Molar teeth of the two rows subequal in size, and equally numerous 



H. paridens. 



Molar teeth of one row wider, and more numerous than those of the 

 other. H. isaaci. 



Helodectes paridens Cope. Sp. nov. 



The smallest species of the family, is of about half the linear dimensions 

 of the Empedocles molar is. It is represented by a left maxillary and proba- 

 bly premaxillary bone, which are so far covered with the adhesive, hard- 

 ened ferruginous mud of the formation, as not to expose a clean surface. 

 The apices of all the teeth are broken off, so that the bases alone remain 

 to indicate their number, form and positions. 



Of the molar teeth proper I count six in the inner, and eight in the ex- 

 ternal row. The two series are close together, and are gently convex in- 

 wards. The bases of the teeth are wide ovals, transversely placed. In front 

 of the eighth tooth of the external row (from behind), are two teeth with- 

 out apparent mates of the internal row (possibly the latter lost). Then fol- 

 lows a tooth of each row, and in front of these another pair, the external 

 being the larger. Anterior to these, the jaw is so split as to remove any 

 teeth of the inner row, if there are any, and one large tooth of the external 

 series stands at the extremity of the fragment. This latter exceeds the 



