AND MESOZOIC FISHES. 
435 
here presents the appearance of having a ininnte denticle on one side separated by 
an attenuated line of base. The surfaces of all the.se teeth are closely and sharply 
grooved from the base to near the apex, which is smooth. Where clear view.s can 
be had, the base of the crown is seen to be round; and although the crowns are 
compressed, there seems to be no cutting edge, and the apex is round and 
needle-like. 
Measurements. 
MM. 
Length of an anteinor crown ; 2 
Length of a median crown ; 4 
Diameter of a median crown at base ; '75 
Length of a posterior crown ; l'5D 
Diameter of a posterior crown at base ; 'To 
Length from extremity of lower jaw to scapula; 1'45 
■ Anteroposterior width of scapula at pectoral fin ; "20 
This spedes was found by Mr. Frederick R. Jelliffe near Galesburg. Ill, in the 
shales of the Coal Measures, at the same locality as that which 3-ielded the Sy»it?to- 
rium and Orodus here described. 
Genus DELTODUS N. & W. 
Dei.todus planidens sp. nov. Plate XX, Fig. 6. 
Two teeth of the inferior series represent this cochliodont shark. One toot li, 
which belongs to the left side, is completely preserved, and shows a transverse in- 
volution which amounts to nearly an arc of 360 °, but of a depressed outline, and 
much more curved, at the apex than at the base as is usual. The surface of the 
crown is distinguished by the absence of ribs and grooves transverse to the di- 
rection of the ramus of the jaw, but the anteroposterior .section is uniformly slightly 
convex. On the other hand it is marked by shallow grooves running parallel to 
the convex internal border, which become more pronounced and closer together as 
the apex is approached. These grooves fade out on the longer or jiosterior border 
of the crown, but terminate abruptly before reaching the anterior border, at the 
internal extremity of the crown. On the external and narrower part of the crown, 
the groov^es extend to both boi’ders. The pores are uniformly distributed over the 
surface. The length of the grinding surface round the curve is 57 mm.; length of 
long chord of tooth, 31 mm.; width of interior base of crown, 30 mm. 
This species belongs to that small section of the genus in which the teeth 
possess longitudinal grooves. In this it resembles D. undulatus and D. cingji- 
latus of Newberry and Worthen. But the teeth of the former species have ribs 
and a wide groove transverse to the jaw; while the latter inncli narrower teeth 
with the pores in bands corresponding to the longitudial (transvere) ridges. 
The present species was found by Mr. W. F. Cummins on Tecumseh Creek, 
northern Texas. 
57 JOXJRN. A. N. S. PHILA., VOL. IX. 
