1917.] NATURAL SCIENCES OF PHILADELPHIA. 165 



The type specimen is quite perfect except that the Up is somewhat 

 crushed in above, making the aperture appear shorter and narrower 

 above than it really is. 

 Oliva dimidiata n. sp. 



The shell is small, cylindric, with conic spire and mamillate apex. 

 The last three to four whorls are flat, covered with callous, and 

 separated by channelled suture. The last whorl is encircled a little 

 above the middle by a narrow groove. The basal fasciole has 6 

 strong ledges. There are 14 short folds on the columellar margin. 



Length 12.2, diam. 5.3 mm.; length of aperture 9 mm.; 6| whorls. 

 Others measure 11.5 and 13 mm. long. 



This was at first suspected to be a young stage of 0. gradata; but 

 that species is longer when it has the same number of whorls. More- 

 over, the narrow ledge of gradata is unlike the groove of this species. 

 It is closely related to the recent 0. undatella Lam. of the west Mexi- 

 can coast but is less inflated, and to judge by the three examples 

 in the typical lot, it does not become so large. 



Type No. 2804. 

 Marginella nugax n. sp. 



The shell is very small, biconic, of four slightly convex whorls; 

 apex obtuse. The suture ascends strongly in front. Aperture 

 narrow. Outer lip broad, thickened, the inner margin having 8 

 teeth, the upper fourth without teeth. Columella with four plaits. 



Length 3.7, diam 2 mm. 



Type No. 2802, A. N. S. P. 



Though very small, the lip has a conspicuous external varix. 

 Mitra tortuosella n. sp. 



The shell is fusiform, slender, with sculpture of acute axial ribs 

 (about 14 on each whorl), the concave intervals between them having 

 spiral impressed lines which do not pass over the smooth summits 

 of the ribs. There are 7 or 8 such impressions in each interval on 

 the penult whorl. On the narrow anterior half of the last whorl 

 there are well separated spiral cords. The outer lip is sculptured 

 within with five slender lirse. There are four columellar plaits. 



Length 18.5, diam. 6 mm.; 8 whorls, the embryonic being lost. 



Type No. 3285, A. N. S. P. 



This is closely related by its sculpture to M. tortuosa but it differs 

 by the very slender form. A young M. tortuosa 16.3 mm. long has 

 a diameter of 7 mm. 



In some of the intercostal intervals there is a median longitudinal 

 groove. 

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