202 ILLINOIS STATE ACADEMY OF SCIENCE 



coalescence of the inner edges of the longer septa, the other four-fifths of 

 the cor£ilIites show no such central eirea, the inner edges of the longer septa 

 uniting irregularly in the central part of the corallite without forming a defi- 

 nite ring. 



Horizon and Locality: — Common in the upper part of the Wapsipinicon 

 limestone in the vicinity of Milan, where it is associated with Phillipsastrea 

 billingsi, Gypidula comis, and the cephalopods described on a later page of 

 this paper. 



RHIPIDOMELLA MINIMA N. SP. 

 Plate II, Figures 1 and 2. 



Description: — Shell small, biconvex, length and width about equal, the 

 greatest width anterior to the middle; hinge line about equal to ^ the greatest 

 width of the shell ; the cardinal extremities rounded. Ventral valve most convex 

 in the umbonal region from which the surface curves rather abruptly to the 

 cardinal margin, and more gently to the lateral and anterior m£irgins; without 

 trace of mesial fold or sinus, beak small, extending only a short distance above 

 the hinge line; cardinal area small, concave, its margins sharply defined; del- 

 thyrium rather broadly triangular. Dorsal valve not quite so convex as the 

 ventral, the greatest convexity posterior to the middle from which the surface 

 slopes gently in all directions, the median portion of the valve depressed into 

 a distinct sinus which begins near the beak, and becomes stronger anteriorly 

 but is poorly defined laterally; the beak is small, not incurved; cardinal area 

 very narrow, lying almost in the plane of the valve. 



The surface of both valves marked by numerous radiating striae which begin 

 near the beak, and bifurcate 3 or 4 times before reaching the front margin 

 where about 3 are present in a distance of one millimeter. These striae are 

 strongest and subangular on the unbones, decreasing somewhat in size towards 

 the front. A few concentric lines of growth are present near the front and 

 lateral margins. 



The dimensions of the shell are: Length 8 to 11 millimeters, greatest width 

 8 to 11 millimeters, thickness 3 to 3.5 millimeters. 



Remarks: — In the small size, and in the mesial sinus of the dorsal valve 

 this species resembles Rhipidomella jerseyensis described by Weller from the 

 Kinderhood of Illinois and Missouri. It differs from that form in its typically 

 smaller size, the more nearly circular outline, the more angular and stronger 

 striae on the unbones, and the fewer and coarser striae over the surface of the 

 shell, the more concave or arched cardinal area of the vertical valve, the less 

 compressed cardinal extremities, and the more rounded front margin which 

 is not emarginate. 



From Rhipidomella dubia (Hall) it is distinguished by the broader posterior 

 portion, more circular outline, longer hinge line, and the presence of a mesial 

 sinus in the dorsal valve, and its absence in the ventral. 



From R. tenuicosta Weller from the Kinderhook our species differs in hav- 

 ing coarser striae, and a more distinct mesial sinus in the dorsal valve. 



Horizon and Locality: — Common in the Cedar Valley stage of the Devonian, 

 along Mill Creek, near Milan, where it occurs a few feet below the Acervularia 

 davidsoni coral reef. 



PUGNOIDES SUBOVATA N. SP. 

 Plate 11. Figures 5, 6 and 7. 



Description: — Shell broadly subovate to subtrigonal in outline, width and 

 length about equal, the greatest width slightly anterior to the middle of the 

 shell. The dimensions of 6 individuals range as follows: Length 8 to 10 mm., 

 width 8 to 10.5 mm., thickness 5 to 8 mm. 



The ventral valve is less convex than the dorsal except at the front, the 

 postero-lateral margins nearly straight, and meet at ihe beak at an angle of 

 nearly 90 degrees, the lateral and anterior margins rounded; the surface is 

 convex in the umbonal region, curving abruptly to the postero-lateral margins, 

 and less abruptly in the anterolateral portion. The beak is pointed, not greatly 



