VEBTEBBATES. 271 



similar in general outline to that of C. intercostatus and C. gomplioides 

 from the same horizon, agreeing with the latter in the vertically arched 

 outline and produced lateral extremities, while the prominence of the 

 protuberances in the anterior basal angles resemble the former form ; 

 but it differs from both of these forms in the central position of the 

 ridge in the postero-superior surface. The crown consists of a strong, erect 

 slightly recurved median cone, and a single pair of strong lateral denti- 

 cles; median cone compressed in front, strongly arched behind, with 

 sharp lateral angles, and gently excavated iu the outer basal region ; 

 lateral cones less compressed or more regularly lenticular in transverse 

 section, produced in front slightly in advance of the median cone, and 

 slightly deflected laterally, in the intermediate angle a faint trace of a 

 rudimentary denticle is observed; the coronal surfaces are smooth, 

 polished, presenting evidences of wear, which may have obliterated all 

 traces of costation except the most obscure vestiges of stria? in the 

 anterior basal region of the principal cone. Lateral diameter of base 

 about .84 inch, antero posterior diameter .33, hight of tooth .T2. 



The tooth above noticed bears a strong resemblance to G. Van 

 Hornei of the St. Louis limestone, although it is distinguishable by its 

 more delicate proportions, greater breadth between the anterior basal 

 angles, and more erect lateral cones. The contour of the base will 

 readily sers-e to distinguish it from individuals of the G. micropus 

 group, which possess but a single pair of lateral denticles ; while the 

 absence of the strong costation so characteristic of G. intercostatus, as 

 also almost equally of C. gomphoides, render its identity with either of 

 the latter forms questionable. Yet we cannot overlook the fact, in view 

 of the superb collections from this horizon, of the singular isolation of 

 the individual here referred to, and which would lead us to seek 

 specific identity with one or other of the above mentioned forms, rather 

 than for evidence corroborating the interpretations based upon a unique 

 and evidently imperfect specimen. 



Position and locality : Upper Burlington fish-bed ; Louisa county, 

 Iowa. 



Cladodtjs eakicostattjs, St. J. and W. 



PL 4, Kg. 18. 



Tooth small. Grown well defined from the base in front, and consisting 

 of a strong, rapidly tapering, laterally deflected, recurved median 

 cone, which is much compressed, sublenticular in transverse section, 

 trenchant, with a triangular depression occupying the base in front, 

 and form lateral denticles on either side, alternating in size, divergent 

 and recurved in nearly the same plane as the median. cone, which 



