REPORT ON THE GASTEROPODA. 333 



Compared with Pleurotoma corpulcnta, 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. From Plcurotoma translucida, Wats., it differs still 

 more in these particulars. From both in its sculpture it is markedly distinct. 



63. Pleurotoma (Thesbia) membranacea, 1 n. sp. (PI. XXVI. fig. 9). 



Station 168. July 8, 1874. Lat. 40° 28' S., long. 177° 43' E. Off New Zealand. 

 1100 fathoms. Blue mud. Bottom temperature 37° - 2. 



Shell. — Singularly unlike a Pleurotoma, being broad, short, tumid, and membrauaceously 

 thin ; it has a short spire of few somewhat tumid whorls, which are parted by a slight 

 horizontal suture ; the surface is smooth and feebly spiralled ; the colour white, under a 

 thin brownish-yellow smooth persistent membranaceous epidermis ; the base is long and 

 gradually contracted, the snout broad and lop-sided ; the sinus lies close up to the 

 suture. Sculpture: Longitudinals — there are fine irregular unequal hair-like lines of 

 growth, which are finely puckered below the suture. Spirals — the whole surface is scored 

 by very slight remote impressed lines, and flat feeble threadlets, which are very irregular, 

 and are interrupted at every biggish line of growth ; just below the suture these are a little 

 feebler, broader, and more regular than elsewhere. Colour white, under a brownish-yellow, 

 smooth, glossy, thin, membranaceous epidermis ; entirely translucent from the excessive 

 thinness of the shell. Spire short-pointed, conical. Apex eroded but evidently small. 

 Wlwrls 5 remaining ; they are short, broadish, and a little tumid, convex, rounded, not 

 keeled, not at all contracted below : the last is large, tumid, and elongated, being drawn 

 out on the base, which is long and rounded; the snout is broad, but is somewhat broker). 

 Suture linear and slight, but distinct in consequence of the junction of the whorls. Mouth 

 semi-lunar, sharply angulated above and below. Outer lip very thin, regularly curved, 

 with a deep wide sinus close up to the suture, whence the front edge of the shell makes a 

 prodigious forward and downward sweep, and then retreats again to the point of the 

 pillar. Inner lip : there does not seem to be even a glaze on the body ; there above, the 

 line is convex, but down the very slightly swollen pillar it runs direct but very obliquely 

 to the left ; the point of the pillar is not truncate, but the sharp edge runs out with a 

 twist, and forms a sharp point at the end of the pillar ; the broad open canal in front 

 seems not to have been in the slightest decree emargnnate. H. 0"87 in. B. 0'53. 



o o o 



Penultimate whorl, height 0*17, breadth of first remaining whorl, 0"03. Mouth, height 

 0-62, breadth 0'28. 



This and Pleurotoma xanthias have a strong general similarity, but differ in all details. There is 

 nothing they so much resemble as Clathurdla pachia ; but that is a very much smaller form, more 



1 So called from its extreme thinness. 



