MOLLTTSCA OE THE i CHALLENGER ' EXPEDITION". 447 



45. PlEUROTOMA (THESBIA) PLATAMODES, n. sp. (7r\a7a/*woi7S, 

 flattened.) 



St. 149 d. January 20, 1874. Lat. 49° 28' S., long. 70° 13' E. 

 Koyal Sound, Kerguelen. 28 fms. Mud. 



Shell. — Thin, fusiform, very finely spirally striated, with a short 

 tumid body-whorl, a high, small, scalar, small-pointed, round- 

 whorled, shallow-sutured spire, a very oblique and scarcely conical 

 base, and a smallish very one-sided snout. Sculpture. Longitu- 

 dinals — there are very slight unequal lines of growth ; and on 

 the lower part of the whorls very slight remote oblique riblets, 

 which entirely disappear on the last whorl. Spirals — fine, very 

 regular and beautiful, sharp, close-set scratchings cover the whole 

 surface. Below the suture a shallow concave trench marks the 

 line of the old sinus ; the lower edge of this broad furrow is de- 

 fined by a slight thread. Colour white. Spire rather high, 

 conical, scalar. Apex small, ending in a flattish, rounded, slightly 

 raised point. Whorls 6, of regular, but rather rapid increase, 

 rounded, without any contraction below : above, each laps up 

 rather high and thinly on the whorl above ; below this they at 

 once swell out tumidly, but hollowed by a slight concave furrow, 

 from which results the scalar rise of the spire ; the last is tumid, 

 but obliquely contracted on the base, and ends in a small trian- 

 gular snout. Suture very slight and not in the least impressed, 

 but well defined by the furrow below. Mouth large, oval, pointed 

 above, and truncate below at the front of the very short canal. 

 Outer lip a little patulous ; in its arch it is a little gibbous 

 above ; the curve of the edge is nearly semicircular, with a high 

 prominent shoulder, between which and close up to the body lies 

 the deep, funnel-shaped, rounded sinus. Inner lip : a thin narrow 

 glaze crosses the body and advances along the pillar, on which it 

 rather early comes to an end, being cut off by the oblique, curved, 

 and thin edge which runs out to the point of the shell : this glaze 

 is defined by a small furrow on its outer margin. The pillar is 

 rather long and straight. H. 04. B. 0*2. Penultimate whorl, 

 height 0-07. Mouth, height 023, breadth 0*11. 



Compared with Pleurotoma corpulenta, Wats., this is a smaller, 

 squatter shell, with a smaller and more scalar spire, whose outlines, 

 too, are more concave ; the body- whorl is much shorter and more 

 tumid, and the base is much more contracted. Prom P. trans- 

 lucida, Wats., it differs still more in these particulars. Prom both 

 in its sculpture it is markedly distinct. 



