MANUAL OF THE MOLLUSCA. 
and a narrow and deep socket; left valve with two unequal 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, 7 species. Hocene. France, Belgium, England. 
ANTHRACOMYA, 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, obleng, 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. Hpidermis strongly 
wrinkled. 
Animal unknown ; probably had a closed mantle and respi- 
ratory siphons. : 
Distribution, 9 species. Coal Measures, associated with 
marine animals. Great Britain, Nova Scotia. 
Faminy XILX.—ANATINID&.* 
RIBEIRIA (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. LL. Silurian, Portugal; Canada, England. 
Famity XXI.—PHCLADID&.+ 
XYLOPHAGA (see p. 506). Sub-genus, Xylophagella, Meek, 
1864. 
Type, X. elegantula. Cretaceous. Dax. 
* See p. 494, 7 See p. 503. 
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