158 GASTROCH ANID. 
The genus Petricola has been associated with this family. 
A couple of specimens of P. lithophaga have been forced into 
the British list which are from habitats altogether apocryphal ; 
the one is stated to have occurred in clay at Bristol, the other, 
from discharged ballast in Cork harbour,— a most suspicious 
receptacle. Those who wish to see an account of this species 
may consult the ‘ British Mollusca,’ i. p. 151, pl. 6. f. 9, 10; 
(animal) pl. G. f. 1. We believe it is not indigenous. 
GASTROCH ANA, Spengler. 
G. mopiotina, Lamarck. 
G. modiolina, Brit. Moll. i. p. 132, pl. 2. f. 5, 6, 7,8; (animal) pl. ¥. £..5: 
Animal clavate anteriorly, attenuated behind; pale brown ; 
mantle closed, except an aperture in front for a small sub- 
cylindrical byssal foot ; the texture is thin on the dorsal range, 
ventrally extremely fleshy, bemg composed on the inner 
surface of thick muscular pale green folds and rugosities. 
M. Deshayes considers these substances secreting glands ; 
others, as ovaria; we concur with that naturalist, and think 
they may produce the matter for the lmings, and the viscous 
fluid for the agglutination of the molecular particles used in 
the construction of the tubular dwellings of these animals, when 
they are not in calcareous deposits. The siphonal tubes are 
elongations of the mantle, soldered on each other nearly their 
whole length, which in the greatest extension are about three 
times the length of the shell, and are even longer in propor- 
tion than those of the Pholades. M. Deshayes observes, in 
his comment on Lamarck, that the tubes are very short 
when the animal is contracted; but this is so in every other 
bivalve under a similar condition ; their colour is pale reddish- 
brown, and both orifices have short cirrhi of an intense rufous 
hue. The branchiz are pale brown, suboval, hanging hori- 
zontally, of small depth, gradually becoming posteriorly more 
linear, having their terminations deposited in the siphonal 
tube; the texture is thin, and they are finely pectinated on 
