VERTEBRATES. 281 



ally obsolete below; anterior face occupied by six to ten strong sharp 

 crested costa?, which increase by implantation, becoming obsolete 

 towards the apex where the exterior pair merge into the lateral mar- 

 gins, producing the sharp cutting angles, strongest in the middle, and 

 towards the base of the cone often swelling into strong plicae, which 

 give off subordinate carina? by bifurcation ; posterior face apparently 

 destitute of stria? or costatiou. A perfect, medium sized tooth will 

 measure in greatest anteroposterior diameter of base .20 inch, lateral 

 diameter .31, thickness .10, hight of cone .32, greatest diameter at base 

 about .12 inch. 



The form here described was first brought to our notice by Mr. 

 Speen t geb, and subsequently fine suites of specimens have been obtained 

 at the localities in the environs of Burlington. They usually occur as 

 strong cusps without the base, which has been worn or broken away. 

 But even in this condition they may be readily identified, the strong 

 costation of the outer face serving to distinguish them from similarly 

 preserved specimens of the forms with which they are associated, L. 

 calceolus. As in the case of the latter form, there occurs in the Keokuk 

 limestone a very similar form of teeth ; but our material from that hori- 

 zon is insufficient more than to establish the fact of the close relation- 

 ship existing between them and the Upper Burlington teeth. A large 

 suite of specimens may disclose differences by which they may be dis- 

 tinguished from each other, such as we have pointed out in connection 

 with the above mentioned form. 



Position and locality : In the fish-bed horizon of the Upper Burlington 

 limestone ; Louisa and DesMoines counties, Iowa ; and localities in Hen- 

 derson and Warren counties, Illinois. The localities in the Keokuk 

 limestone are in the vicinity of Warsaw, 111., Boonville, Mo., where Dr. 

 "Williams has obtained specimens of the Keokuk teeth ; Bentonsport, 

 Iowa. 



Lambdodus calceolus, St. J. and W. 



PI. V, Fig. 5. 



Teeth small. Base moderately thick, elliptical in outline, narrow, 

 greatest expansion posterior to the coronal cusp, in front slightly pro- 

 duced, narrower than behind and rounded, posterior extremity usually 

 obliquely rounded or truncated. The coronal cusp rises from the ante- 

 rior extremity of the base, in a strong, rapidly tapering, conical, slightly 

 twisted cone, which bulges outward, recurved and more or less deflected 

 from a vertical line, in hight probably two-thirds the anteroposterior 

 diameter of the base; the transverse section of the cone is elliptical or 

 sub-oval, the long axis being in the same direction as that of the base, 



