MOLLUSCA OF THE ' CHALLENGER ' EXPEDITION. 103 



3. Cerithitjm (Triforis) hebes, n. sp. 



St. 135. Oct. 18, 1873. Nightingale Island, Tristao da Cunha 

 Islands, S. Atlantic. 100-150 fms. Eock ; shells. 



Shell. — Cylindrically conical, blunt, uncontracted towards the 

 base, strong, translucent, hardly glossy. Sculpture. Longitudinals 

 — on the last whorl there are about 20 longitudinal rows of rounded 

 tubercles, parted by depressions of much the same breadth and 

 form as themselves; they run more or less continuously and straight 

 up the spire from whorl to whorl. There are indistinct lines of 

 growth. Spirals — on each whorl the tubercles are arranged in 

 three spiral rows, parted by rather deep but narrow squarish 

 furrows. The highest row is rather smaller and less prominent 

 than the others. The base of each whorl is sharply but not deeply 

 constricted ; the edge of this constriction appears on the margin 

 of the base as a rounded thread, defined by a slight furrow, which, 

 with the exception of microscopic radiating lines of growth, is the 

 only ornament of the flat and very slightly conical base. Colour 

 pure somewhat translucent white. Spire high and conical, but 

 contracting very little, and hence more cylindrical than usual. 

 Apex very blunt, but almost mucronated ; this arises from the 

 three embryonic whorls, which are smooth, being formed of two 

 tumid threads, of which the lower is the larger, but the upper is 

 at first the more prominent, and at its origin stands up minute, 

 round, and prominent, like a small eccentric blunt spike, remind- 

 ing one of the mucronated mamillary plug of some of the Ccecums. 

 It is not a plug, however, but the true embryonic form. This 

 embryonic shell is smooth and glossy, but has some faint trace of 

 spiral sculpture. Whorls 12, of very gradual increase, flat on 

 the sides, constricted below, flat and hardly conical on the base. 

 Suture well defined by the contraction of the whorl above it, and 

 by a minute thread on which it projects. Mouth angulately oval, 

 with a small straight canal in front. Outer lip broken. Pillar 

 perpendicular, straight, short, narrow, pointed. Inner lip a 

 thickish porcellanous glaze. H. 024. B. 006. Penultimate 

 whorl 0-03. Mouth, length 0'032, breadth 0-02. 



This species has some resemblance to T. suturalis, Ad. & Eve., 

 but is easily distinguished from that by its blunt apex and the 

 less sunken suture. 



4. Cerithium (Triforis) inflattjm, n. sp. 



St. 24. Mar. 25, 1873. Lat. 18° 38' 30" N., long. 65° 5' 30" W. 



