38 THE NAUTILUS. 



with the tooth belong to the genus Pterorhytis Conrad (long called 

 Cerostoma) and those without a tooth have had various names applied 

 to them from Ocinebra to Pteropurpura. Of the allied species M. 

 californicus has scaly spirals of three sizes, ending in sharply pointed 

 channelled recurved varical digitations ; M. trialatus Sowerby has 

 dark brown and white color bands, the shoulder of the whorls ex- 

 cavated, the large posterior digitation of the varices curved toward 

 the apex of the shell, and the varix has no anterior sulcus next the 

 canal. M. carpenteri Dal I, is nearly smooth, thinner than the others, 

 and with no knobs between the varices on t lie whorls. All have 

 similar opercula of muricoid type. 



A NEW LAMPSILIS FEOM ARKANSAS. 



BY JAMES H. FERRISS. 



Lampsilis Simpsoni. 



Shell sub-solid, elongated, slightly obovate, narrowed in front, and 

 rather evenly rounded at both ends, somewhat inflated, having the 

 greatest diameter at the middle and gradually tapering each way to 

 the ends, feebly gaping at the anterior base and behind, beaks rather 

 low but distinct, their sculpture consisting of ill defined, irregular 

 subnodulous corrugations; epidermis well developed, in the young 

 specimens projecting beyond the shell all around, slightly concentri- 

 cally wrinkled, and showing the rough irregular growth lines; tawny 

 with green rays and coppery beaks in the young, brownish or black- 

 ish in the old state ; posterior ridge well marked in the earlier stages 

 of growth. Hinge line evenly curved ; pseudo cardinals reduced to 

 mere stumpy vestiges ; there are two feeble, remote laterals in the 

 left valve and one in the right ; epidermal matter folded in along the 

 hinge line ; anterior cicatrices rather deep, irregular; posterior cica- 

 trices shallow ; nacre shaded violet, bluish and coppery, iridescent 

 behind. Length 95, height 50, diameter 32 millimeters. Spring 

 River, Hardy, Arkansas. 



This specimen seems to stand between Lampsilis tenuissimus and 

 L. gracilis. The former is more compressed, has a stronger posterior 

 ridge, i^ pointed behind, and is inflated at or just behind the center 

 of the base, and gaps more decidedly behind. It has something the 

 form of certain specimens of L. gracilis, but is more elongated and 



