328 PALEONTOLOGY OF ILLINOIS. 



Genus STEMMATODUS, St. J. and W. 



Amongst the collections from the Upper Burlington limestone, our 

 attention was first drawn to a group of teeth, quite numerously repre- 

 sented, but of so anamolous and withal variable character as seem- 

 ingly to indicate representatives of several distinct though closely allied 

 generic groups. Subsequently, however, we have had opportunity to 

 examine a fine lot of these remains in the collection of Mr. Springer, 

 from a single locality, but all as detached or isolated teeth, which has 

 resulted in the conviction that they all probably belong to a single 

 genus, and of which there would appear to be several kinds, varietal or 

 specific. As to the character of these latter forms, whether they merely 

 represent the variableness of the dental elements according to the rela- 

 tive position of the teeth, or really indicate specific distinctions, may 

 remain an open question so long as our material consists of these isola- 

 ted elements of the dental armature. 



These teeth may be arranged under at least two typical subgroups, 

 which, taken by themselves separately, would appear to offer distinc- 

 tive features sufficient to suggest their possible generic distinctness ; 

 but, as we shall attempt to show, these subgroups seem to be connected 

 by a most varied and almost complete gradation, as shown by a large 

 suite of specimens exhibiting the intermediate stages almost uninter- 

 ruptedly. The first of these subgroups above alluded to may be repre- 

 sented by teeth possessing the following general features : Teeth, as 

 seen from above or below, triangular in outline, the anterior extremity 

 forming the more or less acute, rounded angle, one or other of the late- 

 ral margins exceeding in length the opposite side, therefore conclu- 

 sively showing that there were rights and lefts, whether associated in 

 pairs or greater numbers. The basal portion is but slightly produced 

 beyond the coronal region anteriorly and laterally, is generally rounded, 

 possibly by abrasion, into the inferior surface, which latter presents a 

 slightly arched outline between the front and posterior extremities, 

 plane or slightly concave laterally. The crown consists of three or 

 more longitudinal rows of stout, depressed denticles, which originate 

 near the anterior extremity, gradually diverging and increasing in size 

 posteriorly, the individual cusps of the various rows alternating, their 

 apices directed backward, and in worn specimens, especially towards 

 the front, scarcely individualized on account of the attrition to which they 

 have been subjected while in use ; the perfect cusp is more or less com- 

 pressed antero-posteriorly, with more or less well-defined lateral angles or 

 cutting edges, and striated as in Cladodus ; the posterior ones are much 

 produced backward, projecting far beyond the posterior basal border, 



