No. 3.J 



BILLINGS — ON THE GENUS OBOLELLINA. 



329 



Prof. Hall's fip;. 1 rcprcscots the cast of the interior of the dor- 

 sal valve of his Oholus Conradi, showing that the three muscular 

 impressions are completely concealed by two sub-conical projec- 

 tions, just as they are concealed by the cones in TrimereUa. I 

 have lying before me fifteen casts of the interior of 0. GaUensis, 

 and in all of them the three scars are entirely exposed as in fig. 6, 

 below. With all due deference, therefore, I think that 0. Conradi 

 should be classified in TrimereUa rather than in the same genus 

 with 0. Galtensis. 



6 7 



Fig. 6. The original tigure of 0. Galtensis showing the cast of the 

 interior of the dorsal valve. Compare with Fig. 2. The specimen is 

 imperfect hut it shows the casts of the groove dd^ the two large ovate 

 scars, lb, and the smaller pair, c, of fig. 2. 



8. Dorsal valve of Ololellina? magnifica. This was figured in the 

 Keport of the Geological Survey of Canada for 1857, published in 1858 

 as a dorsal valve of 0. Canadensis. It is, however, a distinct species. 

 The following is the description. 



? MAGNIFICA, n. sp. Dorsal valve transversely broad ovate; 

 width about one-fourth greater than the length ; uniformly and 

 moderately convex; apical angle about 120 degrees; cardinal 

 edges nearly straight, or gently convex for about one-third the 

 length of the shell; sides and front rounded, the latter more 

 broadly than the former. The area seems to be obsolete alto- 

 gether or merely linear. • 



The ventral valve is depressed convex with a large beak slightly 

 incurved. Area with a wide triangular pcdimcuhir groove; no 

 lateral furrows. Surfaces of both valves concentrically marked 

 with imbricating lines of growth. 



In a specimen, which appears to have been about 20 lines in 

 length, the height of the area is nearly 3 lines. 



