VEBTEBRATES. 185 



PCECILODUS CESTKIENSIS, St. J. and W. 



PI. VIII, Fig. 15-17. ' 



Teeth of medium or small size, mandibular posterior form having 

 the general trapezoidal outline of Cochliodus, or a great transverse 

 diameter compared with that in the direction of the strongly arched 

 inrollment. Antero-lateral border comparatively short, a distinct 

 furrow denning the narrow enamel fold from the shallow basal rim, 

 sharply inrolled spirally at the extremity; inner margin very oblique 

 in front, joining the articular border at a very obtuse angle, sud- 

 denly rounded at anterior ridge and more broadly so in passing the 

 base of the principal ridge, moderately incurved in the intermediate 

 space, and again on extending into the somewhat produced posterior 

 angle ; postero-lateral border moderately arched and rapidly con- 

 verging toward point of inrollment, coronal enamel forming a rela- 

 tively strong fold denned by a deep narrow sulcus from the inferior 

 basal rim, which projects posteriorly beyond the coronal limits, ter- 

 minating in a more or less produced spur. Anterior coronal ridge 

 nearly as prominent but narrower than that behind, culminating in 

 a sharply rounded crest with steep slopes descending to the antero- 

 lateral border on the one hand, and into the deep, narrow median 

 depression on the other; principal ridge situate about equidistant 

 between the angles of the inner margin, broadly arched transversely 

 over the inner third of its extent, but more sharply rounded in the 

 outer portion, the posterior slope abrupt, and as in the parallel 

 ridge somewhat deeply excavated; posterior depression broad and 

 deep, the transversely slightly concave surface steadily rising into 

 the wide posterior alation, which comprises about one-third the lat- 

 eral diameter of the crown. Surface along the inner margin envel- 

 oped in a glassy enamel layer beneath which the minute densely 

 crowded punctae are distinctly visible, and which are laid bare over 

 the greater area of the triturating surface in front ; faint transverse 

 undulations traverse the crown conforming to the curvature of the 

 inner margin, worn specimens exhibiting more distinct irregular 

 undulations along the crests of the coronal prominences. A speci- 

 men of ordinary size measures across the inner margin 16 mm..; 

 length along principal ridge to inrolled outer margin, 10 mm. ; 

 length of anterior articular border, about 3.5 mm. 



Maxillary posterior teeth subelliptical in outline, strongly inrolled 

 at the outer margin. Antero-lateral border produced obliquely forward 



