126 MOLLUSCA FROM THE CRAG. 



Mont acuta. Turton, 1822. 



Ligula (sp.). Mont., 1808. 



Petri cola (sp.). Gray, 1825. 



Erycina (sp.). Desk., 1825 : (sp.) Nyst, 1 844. 



Mesodesma (sp.). Loven, 1846. 



Generic Character. Shell equivalve, inequilateral, transversely oblong, or obliquely 

 ovate, generally small and thin : surface smooth, or concentrically striated, and 

 occasionally with a few radiating ridges. Hinge with two diverging elongated teeth, 

 more conspicuous in one valve than in the other. Ligament internal, placed in a 

 triangular fossette : impression by the mantle without a sinus. 



Animal oblong, having its mantle open in front, margins not fringed ; without 

 siphonal tubes (?) ; foot large and broad, furnished with a byssal groove. 



The name of this Genus was proposed in honour of Montague, the author of 

 ' Testacea Britannica ;' it is not, however, well determined, as two or three species, 

 the animals of which have undergone a careful examination, so far as their diminutive 

 forms will permit, seem to present considerable differences, and as far as regards the 

 shells alone, or their dental characters, the species here included would probably justify 

 their being separated into different Genera. As the authors of the ' Hist, of Brit. 

 Mollusca' have made the same observation, and have not ventured to propose a new 

 Genus where the animals present characters so materially different, it would ill 

 become the Palaeontologist with only the shells to guide him, to venture upon such 

 a step. 



Shells apparently of this Genus, at least such as present similar dental characters, 

 have been obtained from the Older Tertiaries of this country by Mr. Edwards ; but 

 nothing as yet known have been found in any Deposit of a more ancient date. Its 

 Geographical range is at present limited to the European Seas and the Western Coast 

 of America. 



1. Montacuta bidentata, Montague. Tab. XII, fig. 17, a, b. 



Mya bidentata. Mont. Test. Brit., p. 44, t. 26, fig. 5, 1803. 



— — Mat. and Rack. Linn. Trans., vol. viii, p. 41, 1807. 



_ _ Turt. Conch. Diet., p. 102, 1819. 



Montacuta bidentata. Turt. Brit. Biv., p. 60, 1822. 



— — Gould. Inv. Massacb., p. 59, 1841. 



— — Macgill. Moll. Aberd., p. 302, 1843. 



_ _ Thorpe. Brit. Mar. Conch., p. 52, fig. 58, 1844. 



_ _ Alder. Cat. Moll. North, and Durh., p. 95, 1846. 



— — Forb. and Hani. Hist. Brit. Moll., vol. ii, p. 75, pi. 18, figs 6, 



6a, 1849. 

 Anatina bidentata. Brown. Illust. Brit. Conch., pi. 11, figs. 8, 9, 1827. 



