OF CONCHOLOGY. 213 



species * but now believe them to be well distingaisbed by a 

 difference of color and texture, and by other peculiarities. 



7. GoxioBAsis NiGRiNA, Lea. — t. 24, f. 12. 



Description. — "Shell smooth, small, conical, rather tliin, nearly- 

 black, polished; spire somewhat elevated; suture impressed; 

 whorls regularly convex; aperture small, ovate, angular above, 

 dark purple within; columella incurved, purple. 



Operculum dark brown, the polar point being low down and 

 near to the left margin. 



Habitat. — Clear Creek, Shasta County, California. Dr. 

 Trask. 



Dimeivnons. — Diam. "23 inch, length '67 inch, 



Remarhs. — A number of good specimens, with their oper- 

 cula, were sent to me by Dr. Trask. In form, size and color, 

 this species is very like to Melania semicarinata, Say, from 

 Georgia and South Carolina. It may be distinguished at once 

 by not having the carination of that species, which is usually 

 strongly marked. It is not quite so high in the spire, and the 

 aperture is more rounded at the base. In all the specimens 

 of nigrina which I received, the apex is worn off. In the half- 

 grown ones I can see no disposition to carination or plication 

 in the upper whorls. I should suppose that in perfect speci- 

 mens, the number of whorls woijld be found to be about seven, 

 and that the aperture would be about the third of the length 

 of the shell. In some of the specimens there is a disposition to 

 put on a few fine striie, and in most of them there is a very 

 small angular line running below the suture. I am not ac- 

 quainted with Dr. Grould's Melania silicula and bulbosa from 

 Oregon, described in Proc. Boston Soc. Nat. Hist., July, 1847; 

 but from the descriptions, I have no doubt that they are differ- 

 ent from both species herein described." 



This species is not always so cylindrical in form, as described 

 by Mr. Lea; in specimens from other localities, I find a number 

 with perfect, acuminate spires. In these, the number of whorls 

 is eight. None of these can be properly said to be plicate, 

 one or two imperfect ribs being only occasionally developed 

 in an individual, upon the apicial whorls. The color varies 

 from very dark chesnut to dull greenish, and the interior color 

 varies correspondingly. None are banded. 



The species differs from Draytonii, in its thinner substance 

 and greater polish, and may be distinguished at once from Gon. 

 Bairdiana., by the absence of plicse and of a band. 



I have specimens also from Butte Co., and Napa Co., Cal. 



* "Synonomy of Strepomatidse," species 207. 



