﻿PROSOBRANCHIATA. 



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the shoulder, almost in the margin, is wide, moderately deep, and somewhat three- 

 cornered in shape. 



Specimens occur in the London Clay in which the shell is smaller, the posterior 

 margins of the whorls more roundedly concave, the ribs thicker and less numerous, 

 and the concentric lines much finer and more closely set. I have described these as 

 at variety of P. gentilis, but they may possibly be regarded as a distinct species. 



Size. — Axis, 1 inch and 3-12ths; diameter, 5-12ths of an inch. 



Localities. — Bracklesham Bay, Bramshaw, for the typical form ; Clarendon, 

 Alum Bay (Stratum No. 4, Prestwich), for the variety. 



No. 206. Pleurotoma comma. Sow. Tab. XXX, fig. 2. 



Pleurotoma comma. Sow. 1816. Min. Con., vol. ii, p. 105, t. 146, fig. 5. 



— — ? Phil. 1836. Enum. Moll. Sic, vol. i, p. 200, No. 8. 



— — ? Phil. 1844. Faun. Moll. regn. utr. Sicil., p. 173, No. 11. 



P. testa elongato-fusiformi, turritd, costellatd, concentfice lineatd : anfractibus con- 

 vexiusculis, postice concavis, medio lavibus, et ibi costellas numerosas, curvas gerentibus : 

 aperturd ovatd, in canalem longiusculum, sub-rectum, product d ; sinu ad humerum collocato (?). 



Shell elongated, fusiform, turreted, ribbed, and concentrically lined ; whorls but 

 slightly convex ; almost straight-sided, concave along the posterior margins, smooth in 

 the middle, and bearing round the shoulders a row of close-set short ribs, swelled at 

 the upper part, curved and pointed below, somewhat resembling a comma ; from which 

 circumstance the specific name was taken. The aperture is ovate, and terminates in 

 front in a moderately long and slightly curved canal ; sinus on the shoulder (?). 



The specimen on which this species was founded formed part of a collection 

 which belonged to the late Mr. Holloway, of Portsmouth, and was presented by him to 

 the Portsmouth and Portsea Literary and Philosophical Society. I have myself care- 

 fully searched through the museum belonging to that institution, for the specimen, 

 but without success ; and as I do not know of any other specimen, the above 

 description has been prepared and the figure taken, by the permission of Mr. 

 Sowerby, from those contained in the ' Mineral Conchology.' 



Philippi has referred some shells from the basaltic tufa of Militello, in Sicily, to 

 P. comma ; but in the uncertainty which attends the present species, from the imperfect 

 figure given of it in the ' Mineral Conchology,' and the want of any existing specimen 

 for comparison, the identification must be accepted with hesitation. De Koninck has 

 also erroneously referred to it certain shells from Basele, which Nyst subsequently 

 distinguished as P. crenata ; and the species has been quoted, by both Nyst and 

 Bellardi, but with doubt, as identical with Basterot's P. denticula. To this last-men- 



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