209 



IcilTHYODECTES T1AMATUS, Cope. 



Represented by a considerable number of remains of an individual from 

 the blue Cretaceous shale, near Russell Spring, on the Smoky Hill River. 



The characters which distinguish this species from /. anaides are numer- 

 ous; but they are less marked when compared with those of I. ctenodon, partly 

 because the premaxillary bones of the latter have not been preserved. In 

 the first place, the dentary bones of the two are of equal length, and support 

 the same number of teeth, while the maxillary of/, hamatus is shorter, and 

 supports more teeth ; it is concave at the proximal part of the tooth-line, but 

 is straight in the corresponding part of/, ctenodon. The end of the dentary 

 is furnished with a strong obtuse process or hook directed upward and for- 

 ward, not seen in / ctenodon. The maxillary behind the. premaxillary is in 

 this species thickened, and with two articular surfaces; the proximal looking 

 outward, the distal inward, and separated by an oblique ridge from the con- 

 dyle. In / ctenodon, there is but one smooth surface, gradually narrowing 

 with the thinning of the bone from the condyle. 



The premaxillary is less extended antero-superiorly than in the species 

 already described, but supports, as in it, an articular face. There is no groove 

 behind it, as in /. anaides and Portheus. It displays a surface for osseous 

 articulation to near its extremity on the inner side ; while below it, and on 

 the external face, near the basis of the first and second teeth, the surface is 

 rugose. Maxillary teeth, forty-three. The dentary supporls twenty-five. 

 The anterior hook is obtuse, and rises abruptly to above the apices of the 

 crowns of the teeth. It is knobbed above, and supports a tooth not larger 

 than the others. 



All the cranial bones preserved are not sculptured. 



Portions of the thin flat ventral spines display the delicately-grooved 

 striation already observed, while the trenchant edge is bordered on one side 

 by raised longitudinal striae. The other side is minutely pitted. 



The vertebral are anterior, and without lateral grooves. Three of them 



are m .0G in length; an undistortcd one is a little wider than deep, and the 



cup is m .026 across. 



Measurements. 



31. 



Length of tbc ramus mandibuli 0. 174 



Depth at the symphysis 0. 055 



Depth of the premaxillary (oblique) 0. 043 



Length of the premaxillary (oblique) , 0. 026 



27 c 



