184 PALEONTOLOGY OF ILLINOIS. 



minute punctae, having individually the appearance of a minute 

 central cone surrounded by a slightly raised rim, and collectively 

 arranged in very regular, seldom bifurcating or implanted transverse 

 grooves, separated by angular carinae which appear to form one side 

 of the rims of the medullary tubes. The illustrations convey an 

 accurate idea of the size and relative proportions of the form indi- 

 cated. 



Apparently possessing unmistakable generic relations with Xystro- 

 dus, the species above indicated differs from the Chester species, X. 

 verus, in the details of contour of the articular area of the antero- 

 lateral, and the proportionally greater breadth of the coronal ridge. 

 The unique example described was discovered by Mr. Wm. Gurley, 

 in the shales immediately overlying Coal No. 7, Lower Coal Measures 

 of the Illinois general section at Danville. 



GENUS SANDALODUS, N. and W. 

 SANDALODUS COMPLANATUS, (N. and W. sp.) 



PI. XII, Fig. 1-4. 



Deltodus complanatus, NEWBEBBY and WOBTHEN, I860, 111. Geol. Surv.. II, p. 98, PL IX, f. 4. 

 Trigonodus major, NEWBEBRY and WOBTHEN, 1866, ib. II, p, 112, PI. XI, f. 8, 9. 



The forms originally noticed under the above cited names consti- 

 tute a characteristic group or species of Sandalodus, as much so 

 indeed as does the type of the genus S. Icevissimus, N. and W. The 

 illustrations of this species which are now introduced suffice to show 

 the generic relationship and the probable specific identity of the two 

 forms alluded to in the above synonymy. Both of the above cited 

 descriptions apply to what we regard as probably the posterior form 

 of the mandible, that referred to under the term Deltodus complana- 

 tus representing a crushed and distorted depressed tooth, examples 

 of which are of more frequent occurrence in the collections than are 

 those corresponding with the extremely convex examples which afford 

 the type of Trigonodus major. While these somewhat pronounced 

 varieties seem to be quite distinct, viewed in the extreme examples, 

 a series of teeth like that before us leads to the conviction of 

 their specific identity. 



Besides the teeth referred to the mandibular posterior form, the 

 collections also contain a few examples exactly corresponding to 

 the form which we have referred to the opposed position upon 



