OP CONCHOLOGY 237 



I am indebted to tlie liberality of Prof. Jos. Henry, Secre- 

 tary of the Smithsonian Institution, for the use of the figures 

 illustrating the following descriptions: 



1. GoNiOBAsis occATA, Hinds. — t. 24, f. 1, 2. 



Description. — "Shell ovate, elongate, lutescent; whorls few, 

 rounded, grooved, intermediate ridges narrow, acute; spire 

 eroded above the fourth whorl; aperture caerulescent. 



Habitat. — River Sacramento, California. 



The rounded whorls are ploughed into numerous farrows, 

 and the intervening ridges are comparatively narrow and keel- 

 shaped; the lower part of the aperture is somewhat dilated, 

 and slightly disposed to elongate in the manner of /o." 



Mr. Reeve, and Dr. Brot following him, have fallen into the 

 error of quoting Shastaensis as a synonym, through that proli- 

 fic source of error, "an authentic specimen." The two species 

 are really widely separated in form and ornamentation. The 

 figure of '■'■Shastaensis^'' given by Reeve, from a specimen in 

 the collection of Mr. Cuming, is finer than any specimen of 

 occata that I have seen. 



Fig. 1 represents the usual form of this species ; fig. 2 is a 

 copy of the original figure of Hinds' description. 



It will be noticed that in the above description no mention 

 is made of the elevation of the revolving ridges into irreo-ular, 

 sharp tuberculations. A large series of specimens before me, 

 shows that this tendency to crowded tuberculation graduallv 

 disappears as the specimens are selected that are longer and 

 narrower, and in shells of the dimensions of Mr. Hinds' they 

 are entirely wanting. Another curious variation is in the su- 

 ture, the whorls of the short, obese specimens being bulo-ed 

 out, as though the shell was forcibly compressed in its leno-th, 

 and the suture is deep and well marked; in the longer shells, 

 the whorls are flatter, and the suture indistinct. The lines of 

 growth are very regular, and generally distinct, interrupted 

 by the revolving ridges. As the substance of the shell is 

 thin, the ridges cause corresponding sulcations on the inner 

 surface of the whorls. 



No variation of color is exhibited in any of my specimens 

 and none of them are banded. 



The form of this species varies from length 1, diameter J 

 inches, to length If, diameter |- inch; but the apicial whorls 

 being generally eroded, the shell appears proportionally 

 stouter. 



Has been obtained only in the Sacramento River. 



