420 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.47. 



poorly developed axial ribs which are almost obsolete on the early 

 turns, where they are merely indicated. Of these ribs. 14 occur upon 

 the third and fourth, 16 upon the fifth, 18 upon the sixth, and 20 

 upon the remaining turns. The intercostal spaces are fully twice as 

 broad as the ribs, and are crossed by 4 low spiral bands between the 

 sutures, which are a little wider than the spaces that separate them, 

 rendering the axial ribs feebly nodulous at the junction with the 

 ribs. On the last 2 turns the second spiral cord below the summit 

 spHts, thus forming 5 spiral cords on these whorls. Beginning with 

 the fifth whorl the cord anterior to the periphery makes its appear- 

 ance in the suture as a small spiral band, becoming more and more 

 exposed in the succeeding turns. The spaces inclosed between the 

 the axial ribs and the spiral cords are shallow, impressed, squarish 

 pits on the middle whorls, and elongate pits having their long diam- 

 eter parallel with the spiral sculpture, on the early turns and the last 



2 whorls. Suture moderately impressed. Periphery of the last 

 whorl well rounded. Base moderately long, well rounded, marked by 

 the feeble continuations of the axial ribs and 9 spiral cords, wliicli 

 grow successively narrower from the periphery to the umbilical area. 

 These cords are separated by grooves about half as wide as the cords. 

 A strong varix, forming a decided callus, is j^resent diametrically op- 

 posite the aperture on the last turn. The spiral cords, preceding and 

 extending partly upon this callus, are tinged with dark chestnut 

 brown. Aperture decidedly patulus, ear shaped, slightly channeled 

 posteriorly and decidedly anteriorly; outer lip thin, decidedly ex- 

 panded, evenly rounded, flesh colored with a checkerboard pattern 

 of brown, when viewed by transmitted light, which is formed by 

 squarish brown spots marking the intercostal portion of the spiral 

 cords; inner lip reflected, somewhat sigmoid; parietal wall covered 

 by a thick callus, rendering the peritreme complete. 



The type, Cat. No. 252569, U.S.N.M., and about 2,000 specimens 

 were collected on the eel grass at Chincoteague Bay. The type has 

 11 whorls, and measures: Length, 8.3 mm.; diameter at the aperture, 



3 mm.; and 2.2 mm. at the antepenultimate whorl. 



There are several species of Diastema tied up under the names of 

 Bittium nigrum Totten, and Diastoma varium Pfeiffer. It would be 

 out of place in the present paper to discuss this subject at length, as 

 it is to be dealt with shortly in a forthcoming monograph upon these 

 small shells by Dr. Paul Bartsch, in which the s^monymy as well as 

 the systematic relationship of these shells will be completely dis- 

 cussed. The present species is more nearly related to Diastoma 

 varium Pfeiffer, a truly West Indian species, than it is to the mol- 

 lusk which has been known to us under that name from the shores 

 of the South Atlantic States. 



