MOLLUSCA OF THE ' CHALLENGER ' EXPEDITION. 435 



tened, but regular, curve from the point of the shell to the keel, 

 where the edge forms a little shoulder, between which and the 

 body lies the narrow round small sinus, with its flanged border. 

 Inner lip straight, with a very thin narrow glaze which early 

 runs out to the rim, being cut off by the slightly oblique and 

 twisted edge, which continues with a slight patulous margin to 

 the point of the shell. H. 034. B. 012 Penultimate whorl, 

 height 0-07. Mouth, height 0-15, breadth 0-04. 



The specimen from St. 75 is somewhat broken and rubbed, and 

 is therefore attributed to this species with a doubt ; the identity, 

 so far as means of comparison exist, is close, only the individual 

 whorls are a little broader and shorter. P. (Mangelia) coral- 

 Una, "Wats., is so similar, that I classed this at first as a variety 

 of that other under the name elongata ; but I am now persuaded 

 of their distinctness. In P. acanthodes the embryonic apex is 

 narrower, higher, and sharper, with an indefinite junction to the 

 regular whorls ; in P. corallina it is much more compact, with 

 the whorls more sunken or immersed, broader, and lower, and its 

 junction is very distinctly defined. In P. acanthodes there are 3^- 

 embryonic whorls, which are contracted, also minutely tubercled 

 on the keel ; and the lower part of the whorls is nearly smooth. 

 In P. corallina there are 4 embryonic whorls, which are not keeled 

 and are scarcely angulated, with a very slight contraction into 

 the lower suture ; the riblets are stronger, and extend from the 

 upper almost to the lower suture. P. corallina is a larger, sharper- 

 cut shell, squarer in its lines ; four whorls in it are as long as five 

 in the other, the body-whorl especially being longer and in the 

 base much more elongated and fuller ; and the snout is broader. 



36. Pleurotoma (Mangelia) corallina, n. sp. 



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

 St. Thomas, N. of Culebra Island, Dan. W. Indies. 390 fms. 

 Coral-mud. 



Shell. — High, narrow, with squarish lines, biconical, ribbed 

 and spiralled, of a frosted-white colour and coral-like texture, 

 with a scalar, blunt but small-pointed spire, a smallish body- 

 whorl, a conical base, and a small undefined snout. Sculpture. 

 Longitudinals — there are about 13 ribs on each whorl ; but 

 they do not all exactly answer from whorl to whorl ; they rise 

 feebly just at the suture, but quickly increase in height, more 

 slowly in breadth ; in the sinus-area they are curved ; from the 



