S7 

 ADDITIONS TO "BRITISH CONCHOLOGY." 



By J. T. MARSHALL. 

 Part VII. (continued from p. 41). 



R. membranacea Ad. — Besides having the " pillar furnished 

 near its base with a strong tooth-like projection or fold " (Jeffreys), it 

 seems to have escaped notice that aged specimens, especially of the 

 coarser forms, develop a tooth-like callosity inside the base of the 

 aperture, and more frequently a third one inside the outer lip just 

 below its junction with the pillar. 



var. venusta Phil. — Torbay. The so-called varieties ventricosa 

 and oblouga occur on our coasts. 



Adams' type of R. membrajiacea is supposed to have been the estua- 

 rine form (var. data Phil.), and R. labiosa Mont, to have been the 

 marine one. But Adams' description is not quite clear, and his bad 

 figures no guide ; hence writers have disregarded what could only be 

 guesswork. P'orbes and Hanley adopted R. labiosa Mont., but mixed 

 up the two forms ; while Jeffreys, who pronounced for R. membranacea 

 Ad., adopted the marine form, and gave the local variety elata 

 secondary place. The brackish-water form is altogether unsuitable, 

 as not being the type of a true species, viz., a really typical shell. It 

 is in the same category as Hyalinia pura var. margarltacea, Tellina 

 balthica var. attenuata. Lacuna puteoliis var. expansa, etc. 



R. violacea Desm. — It has been stated that R. violacea is 

 "exclusively Mediterranean,"^ and that the British shell so-called must 

 be re-named R. lilacina Recluz. It is true the "exclusively Mediter- 

 ranean " form of R. violacea, like many other Mediterranean species, 

 is different from the British one, being a more slender and delicate 

 shell. Their specific characters, however, are the same, and they do 

 not need separate names. 



R. COStulata Aid. — Off Loch Ryan, 2of , a fresh specimen. Pre- 

 viously recorded from Lamlash, with a doubt, by Jeffreys. 



A semi-costate form from Torbay can hardly be separated from 

 some of the Mediterranean forms of R. siniilis. The latter species 

 differs from R. costidata in being more oblong, the ribs do not extend 

 so far to the base, and the outer lip is not thickened by a varicose rib'. 



According to Monterosato,^ Alder's name is a year subsequent to 

 ^. ^7^(?r/«/ Recluz (1843). Not R. costidata Risso (1826), which is 

 R. variabilis Miihlf Nor R. costulata S. Wood, which is R, stefanisi 

 Jeffreys. 



1 Dautzenberg and Diirouchouj: : " Moll. S. Malo," Feuille des Jeunes Nat., 1913. 



2 Nomenclatura, p. 56. 



