VERTEBRATES. 167 



and which was originally described as the "third" in the series to 

 which the name Cockliodus costatus was given by Messrs. Newberry 

 and Worthen. 



Viewed from a standpoint taking cognizance of such features as 

 they possess in common, the form here alluded to offers marked 

 resemblance, in the co-adaptation of the articular borders, to the 

 form described by Messrs. Newberry and Worthen as the "second" 

 tooth of Cochliodus costatus. Essentially the same contour and reversed 

 curvature of the articular borders obtain in the two forms which are 

 otherwise unusually like in coronal contour, so much so indeed as 

 rather to lead to the conclusion that they are distinct species of the 

 same representative form, so little do they differ one from the other 

 in outline and contour; while in Cockliodus the mandibular median 

 tooth widely differs in both these respects from the posterior tooth 

 with which it was associated. Also, there is an appreciable differ- 

 ence in the punctation of the forms here referred to, that of 

 "Cochliodus costatus" being coarser and more irregular, and the 

 general surface contour more uneven and rugged. 



We are at a loss to assign the form here particularly alluded to 

 to any of the recognized generic groups. The extreme involution of 

 the outer extremity and the obliquity of the postero-lateral border 

 do not suggest intimate relations with the median form of Cochli- 

 odus ; on the contrary, those features, together with the general out- 

 line and conformation of the coronal region, are more consistent 

 with the Deltodi, perhaps having closest generic relations with Del- 

 todopsis, with the mandibular posterior teeth of which it agrees in 

 the obliquity of inrollment, narrow alation, and character of the 

 lateral borders. 



Geological position and localities: Upper Burlington limestone, 

 fish-bed strata ; Burlington, Pleasant Grove, Buffington Creek, Louisa 

 Co., Iowa; Quincy, 111. 



DELTODOPSIS ? INFLEXUS, St. J. and W. 



PI. XI, Fig. 13. 



Teeth obliquely trapezoidal in outline, strongly arched and spirally 

 inrolled. Lateral borders converging toward outer margin at an 

 angle of about 25 ; antero-lateral border somewhat obliquely produced 

 outward and forward from the obtuse inner angle, character of 

 articular edge not known ; postero-lateral or oblique border gently 

 arched and more or less sinuous, basal portion greatly thickened 



