158 



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, pi. 6. f. 9, 10; 

 (animal) pi. G. f. 1. We believe it is not indigenous. 



GASTROCH^NA, Spengler. 



G. MODIOLINA, Lamarck. 

 G. modiolina, Brit. Moll. i. p. 132, pi. 2. f. 5, 6, 7, 8; (animal) pi. F. f. 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, being 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 linings, 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 branchiae 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 



