334 THE VOYAGE OF H.M.S. CHALLENGER. 



elongated, and has the cross-hatched apex of Clathurella. I have called them Thesbias for a sub- 

 genus, having small regard for such subdivisions, and knowing, like others, as yet too little about the 

 deep-sea forms to attempt to classify them for myself. Probably they do not at all belong to this 

 group, but they cannot well go elsewhere at present. 



64. Pleurotoma (Thesbia) xanthias, 1 n. sp. (PI. XXVI. fig. 10). 



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

 1 100 fathoms. Blue mud. Bottom temperature 37°"2. 



Shell. — Bather like the young of Columbella rustica, Linne, being oval, biconical, and 

 a little tumid ; the spire is high and conical, the base long and pointed ; the surface is 

 smooth and feebly spiralled, and white. Sculpture : Longitudinals — there are fine hair-like 

 lines of growth, which are slightly puckered below the suture. Spirals — there is a blunt 

 carination in the middle of the whorls, below which the surface is scored with flat threads 

 parted by slight irregular lines ; above the keel on the shoulder these spirals are wholly 

 absent. Colour white, with a glossy surface. Spire high, conical. Apex has probably 

 3 to 3tj whorls, but the extreme tip is broken and only 2 remain ; they are yellow and 

 conical, and are microscopically scored by minute narrow raised lines which are straight 

 above, but below slope very obliquely to the left ; they are not reticulated as in Clathurella. 

 Whorls 4£, below the apical nucleus ; they are feebly angulated in the middle ; the last 

 is large, tumid, and has a swollen base prolonged into a broad triangular lop-sided snout, 

 which is not at all emarginate in front. Suture very slight indeed, but distinct. Mouth 

 narrowly oblong, pointed above, and having no canal in front. Outer lip thin, flatly 

 arched, with a deep broad sinus which lies up at the very suture, and with no shelf at the 

 insertion; below the sinus the edge of the lip sweeps forward in a great wing- like curve. 

 Inner lip : there is a mere thin glaze on the body ; its line is barely convex on the body, 

 subangulatedly concave at its junction with the pillar, which is longish, oblique to the left, 

 and slightly truncate at the point. H. 0*77 in. B. 0'4. Penultimate whorl, height 0'13, 

 breadth of first remaining whorl, 0*03. Mouth, height 0'47, breadth 0"2. 



The mouth is somewhat broken and the shell considerably obscured by an Actinia which has 

 enveloped it. This species has a strong general likeness to Pleurotoma (Thesbia) memhranacea, Wats., 

 but is smaller, narrower, less ventricose, with a higher spire and keeled whorls. From Clathurella 

 pachia, Wats., which is also very like this species, it differs in being larger, broader, with keeled 

 whorls and a scored, not reticulated, apex. Probably those who have not seen the shells will be 

 tempted to unite these species, but when actual specimens are examined the essential differences are 

 very striking. 



1 %a>8iag, yellow head, so called from the colour of the tip. 



