112 



Contributions to Paleontology. 



OBOLELLA ? POLITA. 



PLATE I. FIGS. 17-21 



Obolus apollinus: Owen (not Eichwald), Loc. cit. 



Lingula ? polita : Annual Geological Report, Wisconsin, 1860, p. 24. 



: Owen Geol. Rep. Wisconsin, Vol. i, p. 21 and p. 435. 



Shell small, short ovate, length and breadth nearly or 

 quite equal ; the greatest width near the front, which 

 is broadly rounded. Valves moderately convex, with 

 prominent umbones, somewhat inequivalve ; beaks ob- 

 tuse, one usually a little truncate or emarginate. Surface 

 smooth, sometimes glabrous, with concentric striae : shell 

 calcareous ?, thick, fibrous or lamellose. 

 The interior of the ventral(?) valve has a broad some- 

 what cordiform subcentral duplicate muscular impression, 

 with a raised margin. From the centre beneath the beak 

 extends a low flatly rounded ridge, which reaches into and 

 partially divides the muscular impression. On each side 

 of this low ridge is a nearly flat slightly elevated plate or 

 thickening of the shell, which, extending forward, is con- 

 tinued in its outer limbs in a raised border nearly around the 

 muscular impression ; giving to the whole a broad spatulate 

 form, leaving a space in front where the shell is marked by 

 a few radiating or vascular impressions. On each side of 

 this central elevated plate, and at the anterior extremities 

 of the cardinal line, are two smaller muscular impressions. 

 There is a narrow groove beneath the apex of the valve, 

 and on each side of this an elongate thickened boss or 

 pad. 



The dorsal (?) valve has a narrow central muscular im- 

 pression, the limits of which extend in an acute point 

 below the middle of the shell : on each side is a broader 

 limited area, reaching two-thirds the length of the shell, 

 and extending into the cavity beneath the beak. The 

 whole presents an elongate somewhat cordiform area. No 



