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THE NAUTILUS. 



JULY, 1896. No. 3 



OX THE AMERICAN SPECIES OF EEVILIA. 



BY WM. U. BALL. 



Very little attention seems to have been given to the genus Ervi- 

 tlfi, which is composed of small, rather solid shells which are, in the 

 recent species, frequently brightly colored, concentrically or radially 

 striated or smooth. The soft parts are still unknown though the typ- 

 ical species appears to he common in the West Indies, and the largest 

 known species is found in British and Mediterranean waters. In the 

 forms which are normally concentrically striate or grooved it often 

 happens that some of the specimens have the umbonal portion nearly 

 smooth, the normal sculpture appearing only when the shell is half 

 grown ; there are also light modifications of the outline, coming 

 within the range of individual variation. In examining the recent 

 forms of North America and the West Indies for comparison with 

 the fossils, the following were recognized, though the small size of the 

 shells and their general similarity of form renders it necessary to 

 study them under a magnifier with the greatest care and attention in 

 order to grasp the distinctive features. 

 Ervilia nitens (Mont.) Turtun. 



This species has the valves somewhat compressed, coarsely, 

 evenly, concentrically grooved, with faint, radial st rial ions on the 

 dorso-posterior surface, both ends somewhat attenuated, the posterior 

 longer and more attenuated, the base evenly arched, the anterior 

 end shorter, higher, with a steeper dorsal slope; the shell rather 

 solid with a robust hinge; the pallial sinus narrow, angular hi 



