284 PALEONTOLOGY OF ILLINOIS. 



Lambdodtjs eeflexus, St. J. and "W. 



PI. V, Fig. 25. 



Teeth of small size. Base broad, apparently rectangular, laterally 

 and posteriorly expanded, considerably produced in front beyond the 

 base of tue cornua and broadly rounded, margin thin, inferior surface 

 slightly concave, both surfaces irregularly striated or roughened. Coro- 

 nal cusps strongly recurved, slightly twisted, gradually tapering to an 

 acute point, laterally compressed, ovate in transverse section with the 

 broad inargiD anterior, apparently smooth and polished. Elevation of 

 tooth about . 27 inch, lateral diameter of base about .30. 



The single example of the above form at present, known, unfortu- 

 nately, does not preserve the entire outline of the base, especially the 

 posterior border, although in other respects it is quite perfect, permit- 

 ting satisfactory comparison with other allied forms. Of the latter L. 

 eostatus, from the Upper Burlington limestone, bears the most intimate 

 resemblance to the form under consideration, which, however, is distin- 

 guished from that species by its thinner base, which is more prominently 

 produced along the front border, and the more strongly recurved cone. 

 With L. transversus, from the St. Louis limestone, it agrees in the cen- 

 tral position of the coronal cusp, but differs in a marked degree in other 

 particulars, as its more slender or much higher cusp, which latter is 

 laterally instead of antero-posteriorly flattened, as in that form. The 

 apparent smooth surface of the cone may be due to attrition, but there 

 is no evidence of costation or other superficial ornamentation. 



Position and locality : Upper fish-bed of the Chester limestone ; Ches- 

 ter, Illinois. 



Ge^us HYBOCLADOD US, St. J. and W. 



The collection from the Upper Burlington and Keokuk formations 

 afford a few examples of a group of teeth, which presents certain pecu- 

 liar combinations of external features not hitherto observed in the den- 

 tal remain's of the Hybodonts of the Lower Carboniferous epochs. They 

 consist of strongly cuspidate teeth, with a broad, posteriorly expanded 

 base, in which last respect they exhibit an unmistakable affinity to 

 Cladodus ; but differing so widely in other and no less important particu- 

 lars, as to leave little doubt as to their distinct generic character. 



Teeth attain medium size. Base elliptical in outline, vertically arched 

 between the extremities, which are more or less sharply rounded, ante- 

 rior face nearly straight, curved laterally, terminating below in a well- 

 defined marginal border or ridge, posterior margin broadly rounded, 



