156 PALEONTOLOGY OF ILLINOIS. 



in the National museum, at Washington, the loan of which, for ex- 

 amination, was kindly procured us by Dr. CHAKLES A. WHITE. 



Geological position and locality: Carboniferous limestone, probably 

 of the age of the Coal Measures ; Grand canon of the Colorado, Utah 

 territory. 



DELTODUS PROPINQUUS, St. J. and W. 



PL X. Fig. 3, 4. 



Mandibular posterior teeth sub-trigonal or sub-spatulate in outline, 

 rather strongly arched longitudinally, with slight, spiral inrollment. 

 Antero-lateral border sigmoidally curved, strongly inbeveled, and oc- 

 cupied by a wide enamel fold, which is sharply denned by a deep, 

 narrow furrow from the extremely narrow basal rim; postero-lateral 

 border converging, at an angle of 35 more or less, to the opposite 

 border, also gently curved, coronal enamel forming a prominent, 

 rounded fold, inbeveled to the sulcated, moderately deep basal rim, 

 which was apparently continued posteriorly into a spur-like angle ; 

 inner margin sigmoidally curved, broadly arched around the base of 

 the coronal prominence, in breadth exceeding the length of the an- 

 terior articular border, inferiorly inbeveled. Coronal prominence oc- 

 cupying three-fourths of the area, rather strongly convex laterally, 

 broadly rounded along the crest, which lies a little anterior of the 

 median line, the wide anterior slope rounded into the anterior border, 

 posteriorly steeply inclined into the narrow depression on that side, 

 denned along the posterior border by the narrow, rounded, mod- 

 erately-upraised alate lobe. Coronal surface traversed by rather 

 strong, irregularly-spaced, transverse undulations and longitudinally 

 marked by less distinct plications ; the dense, polished enamel also 

 presents a delicate rugose appearance, the minute ruga3 having a 

 longitudinal direction; worn surfaces over the outer portion of the 

 crown reveal the usual pitted structure, the punctse becoming con- 

 fluent, or usually longitudinally elongated in the hollows of the 

 transverse undulations. A large tooth shows a transverse diameter 

 across the inner margin of 35 mm ; length of anterior articular border 

 from the obtuse inner angle to the point of inrollment, about 27 mm. 



Mandibular median form known only from a couple of fragments, 

 too imperfect for figuring. It is characterized by the prominence 

 of the anterior lobe, which presents a rounded crest defined on either 

 side by exceedingly abrupt declivities, on the one hand descending 

 to the anterior border which is margined by an obscurely defined 

 narrow fold strongly inbeveled to the deeply-channeled basal rim, 



