12 



AMERICAN JOURNAL 



Gadinia reticulata, H. & A. Adams. Gen. Rec. Moll, i, p. 



463. 

 Roivellia, sp. Cpr., Suppl. Rep. Br. As., 1863, p. 651. 

 Rowellia radiata, Cooper, Proc. Cal. Ac. Nat. Sciences, 



1865, p. 188, (test, jun.) Geogr. Cat. Moll. p. 24, No. 



460, 1867. 

 Siphonaria reticulata, D'Orb., Voy. Am. Mer. v, p. 682. 



Testa subcircularis ; apice centrali ; colore albo vel ex albo 

 virens ; superficies xxx costis radiantibus dichotomis induta, 

 per lineas concentricas cruciatis ; intus alba vel livida. Margine 

 simplice ; in jun. crenulato ; fovea siphonali bene^mpressa, mar- 

 gine prope extremam foveam, parum inciso. 



Shell normally almost circular ; depressed conical ; white or 

 livid, sometimes tinged by the growth of a green or pink nulli- 

 pore. The upper surface marked with from thirty to fifty ra- 

 diating strise or riblets, which are reticulated by the coarse, 

 somewhat elevated lines of growth. The margin in young shells 

 is denticulated, but with age this character is lost. The edge is 

 usually irregular and owes its form to the locality where the 

 animal was stationed ; the notches corresponding to the irregu- 

 larities of the surface where the animal lived. The interior is 

 usually polished, except on the muscular impressions, which are 

 granulous and strongly impressed. The scar is horseshoe-shaped, 

 the right anterior limb broad near its extremity. Close to the 

 anterior extremity of the left limb is a small oval scar indicating 

 an attachment of the mantle to the shell. 



The apex is posteriorly curved, sub-central, smooth, and in the 

 youngest specimens 1 have seen exhibits no tendency to spiral 

 growth. In older specimens it is usually somewhat eroded. The 

 texture of the shell is exceedingly solid, porcellanous and strong. 

 Old individuals fill up the cavity of the apex while adding to the 

 margin. From the irregularities of their stations most fantastic 

 forms occur. The most elevated specimen had an altitude of 

 0*45 in. to a longitudinal diameter of 0*56 in. One of the most 

 depressed measured 0"36 in. high and 0-98 in. long by 0-96 in. 

 wide. In one old specimen the thickness of the shell at the 

 apex was 0-32 in. The young shells are usually quite thin, 

 averaging about 0"04 in. 



My specimens were identified by Dr. Cooper as his Rowellia 

 radiata. The living specimens obtained by him were very 

 young. The adults were examined by Dr. Carpenter, who is 

 disposed to consider them identical with Sowerby's species, which 

 came from Lower California. 



Soft Parts. The external parts are of a livid white. The 



