PROSOBRANCHIATA. 201 



seven or eight, exclusive of the pullus, rounded at the shoulders, nearly straight on the 

 sides, somewhat produced in front, and very slightly bent backwards. The concentric 

 lines are equal, not very distant over the middle of the whorls, but varying in that 

 respect in different individuals ; more crowded at the base and on the shoulders, distant 

 on the posterior margins, which are much elevated, and pressed against the preceding 

 whorls ; occasionally on the last whorl of mature specimens additional faint lines 

 appear. The spaces between the lines are very slightly concave, and finely crenu- 

 lated by the lines of growth, which are very perspicuous over the whole surface of 

 the shell. The aperture is narrow, straight, except at the base, where it is a little 

 deflected, and scarcely emarginate ; the outer lip thin and sharp on the edge, very 

 much thickened within, faintly crenulated on the inner margin by the concentric lines, 

 of a roundedly elliptical shape, and detached from the suture by a wide but very 

 shallow curvature. The anterior margin of the columellar lip is elevated and pro- 

 longed in front, where it serves as the wall of the rudimentary anterior canal formed 

 by the produced base of the shell. 



In specimens from Brockenhurst and Lyndhurst, the middle and upper parts of 

 the whorls are perfectly smooth, with the exception of a single furrow which traverses 

 the posterior margins; and the base of the shell presents numerous shallow furrows, 

 which extend almost up to the middle of the whorl, instead of the sharp elevated lines 

 which characterise the typical form. 



This well-known species, peculiar, I believe, to the Hampshire basin, forms the 

 type of Mr. Swainson's genus Conorbis. In the elevated conical spire, the almost 

 semicircular form of the outer lip, and the produced base of the whorls, it presents 

 the closest analogies with that section of the Pleurotomse formed of P. prisca, P. 

 amphicotius, P. linearis, and similar species. Indeed, so closely does it approach to 

 some of these, that, judging from external characters only, it is difficult to decide to 

 which genus it should be referred. The straight, narrow aperture, however, is cer- 

 tainly that of a cone, and indicates a necessity that the animal, in order that it might 

 withdraw into the inner whorls, should be enabled to enlarge the space within the 

 shell; a necessity which, as I have already stated, was met by the power of absorp- 

 tion possessed by the animal. The curvature in the outer lip, also, is quite distinct 

 in its character from the sinus in the outer lip of the Pleurotomse. 



Size. — Type — Axis, 1 inch and 1-12; diameter, 5-12ths of an inch. Var. — Axis, 

 1 inch and 3-12ths; diameter, 6-12lhs of an inch. 



Localities. — Barton, Alum Bay (No. 29, Prestwic/i), Lyndhurst, and Brockenhurst 

 (New Forest). 



