PAPERS ON GEOLOGY AND GEOGRAPHY 205 



produced beyond that of the dorsal valve, only slightly incurved, closely ap- 

 pressed over the beak of the opposite valve so as to conceed the foramen; 

 mesial sinus obsolete in the posterior part of the shell, but becomes rather 

 broad and deep in the anterior portion where it is produced in a rather broad 

 linguiform extension that cur\es strongly towards the dorsal valve. The 

 anterior part of the shell bears low. rounded plications of which 3 to 5 are 

 depressed in the mesial sinus, on each side of which 3 weak ridges are visible 

 for a short distance on the antero-lateral slopes. 



Dorsal valve more convex than the ventral, the greatest convexity along the 

 middle part, from which the surface curves rather steeply to the postero — and 

 antero — -lateral margins, and much less strongly towards the front margin; a 

 broad, low. mesial fold appears in the posterior half of the shell, becoming well 

 de5ned, and distinctly elevated at the front where it receives the extension of 

 the opposite valve ; near the front are a few low. rounded radiating ridges. 4 

 to 6 of which are elevated on the mesial fold which is well defined, and is 

 bordered on each side by 2 or 3 weaker ridges, none of which extend to the 

 middle of the valve. 



Besides the short, low. rounded, radiating ridges and furrows, the surface is 

 marked by numerous fine concentric lines which are visible with a lens; a few 

 stronger lines of growth are also usually present. 



Remarks: — This shell is easily distinguished from Pugnoides pugnus. and 

 Pugnoides pugnus var. alta. in the weak and rounded character of the radiating 

 plications, in which characters it more closely agrees with forms like Pug- 

 noides ottumwa of the Ste. Genevieve limestone, of Mississippian age. It 

 differs from the latter species in being much shorter and thicker in proportion 

 to its length. 



Horizon and Locality: — It occurs abundantly in the Cedar Valley limestone, 

 a few feet above the Acervularia davidsoni coral reef, about two miles east of 

 Andalusia, in Rock Island County, Illinois. 



CRANAENA SUBOVATA N. SP. 

 Plate II. Figures 9 and 10. 

 Description: — Shell subovate to subtriangular in outline, longer than wide, 

 the greatest width anterior to the mid-length, the postero-lateral margins 

 nearly straight, converging to the beak at an angle of about 75 degrees; an- 

 tero-lateral margins rather strongly and regularly rounded, front margin trun- 

 cate or nearly straight. The dimensions of a shell of about average size are: 

 Length of ventral pedicle valve 17 mm. ; of dorsal valve. 14.5 mm., greatest 

 width 14 mm., convexity 9.5 mm. 



Surface of ventral valve arched along the meridian line from beak to front, 

 the greatest convexity slightly posterior to the middle where a faint depression 

 appears, and increases in prominence toward the anterior margin where it 

 forms a broad, shallow, poorly defined mesial sinus. In the posterior part of 

 the shell the transverse curvature is rather strongly convex, being inflected a 

 little toward the cardinal extremities; the curvature is more gentle on the 

 anterior and antero-lateral portions of the valve: the beak is truncated, not 

 strongly incurved, perforated with a moderately large foramen; delthyrium 

 concealed by the beak of the opposite valve. 



Dorsal valve about as convex as the ventral, the greatest convexity posterior 

 to the middle, gently arched from the beak to the front margin; the transverse 

 convexity greatest in the posterior portion, the surface curving rather steeply 

 from the median line to the cardinal and lateral margins, and more gently over 

 the anterior and antero-lateral areas: no mesial fold or sinus present; beak 

 pointed, and incurved beneath that of the ventral valve. 



The surface of both valves is marked by numerous, well defined concentric 

 lines of growth which vary in number, strength, and distribution in different 

 shells. Shell structure punctate. 



