PELECYPODA—PRIONODESMACEA. 385 



31. S. modesta Ulrich. (Fig. 489, c.) Ordovicic. 

 Quite small, obliquely ovate. 



Lower Galena : Wisconsin, Minnesota. 



32. S. ventralis Ulrich. (Fig. 489, a-b.) Ordovicic. 

 More nearly circular than 5. modesta. 



Upper Cincinnati Group : Wisconsin, Minnesota. 



XIII. Pal^anatina Hall. 

 Left valve larger than right. Elliptical, with short anterior and 

 longer posterior end. Beaks low, that of left valve rising above 

 that of right. Umbonal slope prominent. Valves crossed from 

 beak to base by a shallow depression ; both umbonal ridge and 

 depression less prominent in right valve. Surface covered with 



FlG. 489. a, b, Saffordia ventralis, view of left valve ; c, Saffordia modesta, left view 

 of internal mold ; d, e, Psiloconcha grandis, left and cardinal views. (Minn. Surv.) 



fine concentric striae. Hinge with two slender processes beneath 

 the beak. Pallial line simple. Devonic. 



33. P. typa Hall. (Fig. 488, b-c.) Devonic. 



Left valve somewhat gibbous at umbo. Right valve depressed- 

 convex. Beaks anterior to middle. 



Chemung Group : New York. 



XIV. Tellinopsis Hall. 

 Elliptical, with rounded anterior and truncate or emarginate 

 posterior end. Beaks small, subcentral. Umbonal slope promi- 

 nent. Surface marked with concentric striae and weak radiating 

 striae. Hinge without teeth. Ligament external. Muscular im- 

 pressions shallow. Devonic. 



