210 PALEONTOLOGY OF ILLINOIS. 



referable to the lower jaw is apparently subquadrangular in outline, 

 the coronal surface regularly transversely arched into the low prom- 

 inence which occupies the greater part of its area, a shallow de- 

 pression extending along the outer border; the coronal belt in the 

 anterior margin and inner border extends one-fourth or one-third 

 the depth, and is marked by delicate vertical rugosities, and dis- 

 tinctly denned from the basal portion, the posterior and outer sidfs 

 unknown. The surface of the crown presents an elaborate sculp- 

 tured appearance from the delicate rugosities which are disposed in 

 longitudinal lines, a narrow worn belt along the anterior edge ex- 

 posing the minute punctate structure, the surface here also showing 

 faint transverse undulations. The supposed maxillary form prese?its 

 a broad shallow concavity in the transverse diameter, and very 

 gently arched longitudinally, '.the enamel forming a well-defined belt, 

 deeper along the inner articular border than at the anterior ( ?) mar- 

 gin, which is rather strongly inbeveled. The coronal surface presents 

 an exceedingly intricate rugose ornamentation, the rugosities appar- 

 ently not conforming to any definite direction. The examples attain 

 a breadth of 40 to 50 millimetres, but they are too imperfect to show 

 details other than those noticed. 



The first noticed form bears marked resemblance to the corre- 

 sponding form of Psammodus Lovianus in outline and contour, so far 

 as these features are decipherable, and the peculiar rugose ornamen- 

 tation of the coronal surface may be that of a tooth which has been 

 less exposed to wear than the examples noticed under the latter 

 specific designation. Still the present tooth differs from that form 

 in having a more angular inner border, the crown in P. Lovianus 

 being rounded to the enamel belt of the articular border. In rela- 

 tion to the companion tooth described above, its mutilated condition 

 hardly affords the necessary data for the restoration of its outline and 

 coronal contour, but the beautiful ornamentation of the surface is well 

 displayed. In the latter character the tooth departs so widely from 

 the specimen with which it is provisionally associated that we are 

 inclined to regard their specific identity as improbable. In the pe- 

 culiar sculpturing of the coronal surface it bears greater resemblance 

 to the Keokuk species, P. grandis, though the disposition of the 

 rugae is much less regular than obtains in the latter species. 



The same formation affords a fragment of a small tooth belonging 

 to the form individuals of which we have elsewhere noticed under 

 the specific designation Psammodus crassidus. The specimen preserves 

 only a part of the outer border, which shows a somewhat oblique 



