MANUAL OP THE MOLLUSOA. 



and a narrow and deep socket ; left valve with two tineqnal teeth 

 separated by a large socket. Ligament internal, pallial impres- 

 sions simple, slightly inflected posteriorly. 



Animal with the mantle united behind, margins of the 

 mantle with duplicate foliaceous tentacles; foot compressed, 

 triangular; siphons short, united at the base, the incurrent 

 tube the larger and more elongated, the opening of which is 

 surrounded by arborescent tentacles. 



Distribution, 3 species. Mediterranean. 



Fossil, 1 species. Eocene. France, Belgium, England. 



Ajstthracomta, Salter, 1861. 



Etymology, anthrax, coal, and mya, a generic name. 



Synonym, Naiadites, Dawson. 



Type, A. Adamsi, Salter. 



Shell thin, equivalve, the right valve rather larger; valve 

 close, oblong, wider behind, where there is a blunt siphonal 

 ridge ; rounded anteriorly, with a byssal sinus on the anterior 

 ventral edge. Beaks small, anterior, and slightly prominent, 

 with an obscure lunette ; posterior hinge line with a narrow 

 interior ridge ; ligament external. Epidermis strongly 

 wrinkled. 



Animal unknown ; probably had a closed mantle and respi- 

 ratory siphons. 



JDistrihution, 9 species. Coal Measures, associated with 

 marine animals. Grreat Britain, Nova Scotia. 



Eamily XIX. — ^Al^ATESriD^.* 

 EiBEiRiA (see p. 497). 



Mr. Billings describes in this genus, ''beneath and in front 

 of the umbo, a small aperture of a semicircular shape, which 

 appears to be the entrance to a tubular passage running back- 

 wards over the transverse plate into the general cavity of the 

 body." He regards it as a byssal orifice. 



Mr. J. W. Salter referred this genus to the class Crustacea. 



Fossil, 4 species. L. Silurian, Portugal ; Canada, England. 



Family XXI. — PnoLADiDiE.t 



Xtlophaga (see p. 506). Sub-genus, Xylojphagella, Meek, 

 1864. 



Type, X. elegantula. Cretaceous. Dax. 



* See p. 494. t See p. 508. 



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