GASTROCII^NA. 135 



anteriorly, tapering posteriorly, the siphonal tube capable 

 of considerable extension. The mantle is entirely closed, 

 with the exception of a small aperture in front, for the 

 passage of the small finger-shaped pointed foot, which has 

 a byssal groove at its base. That part of the mantle which 

 is exposed is strong and thick. " Its inner surface," writes 

 Mr. Clark, " is fortified by a muscular substance of a pale 

 green colour, disposed in folds and rugosities." This is 

 probably the same body which M. Deshayes regards as an 

 acid-secreting organ. The siphonal tubes are capable of 

 being either almost withdrawn into the shell or protruded 

 to three times its length. They are united almost quite 

 to their extremities. Both the orifices are surrounded by 

 cirrhi. These, according to Philippi, are short and red, 

 and appear to spring from the margin of the opening in the 

 lower siphon, but are removed to some distance from it in 

 the upper.* Mr. Clark describes the branchiae as of a pale 

 brown colour ; they run longitudinally, and nearly parallel 

 to each other, and are of small depth, the upper one less 

 than the lower. On each side of the mouth is a pair of 

 short finely-pectinated tentacula, nearly equal in length. 

 The body of the animal is of a flaky white hue ; the siphons 

 reddish brown, more deeply coloured at their extremities. 



With regard to its locality, we look upon Torbay as the 

 most prolific seat of it upon the English coast, and Birter- 

 buy Bay, in Connemara, as the most populous of its Irish 

 habitats. From the former, at the depth of ten fathoms, 

 we have taken masses of limestone well honeycombed by 

 its excavations, and tenanted by several individuals, both 

 •living and dead ; from the latter came numerous examples, 

 dredged by Dr. Farren and Mr. Barlee, of that interesting 

 variety with the more elaborate case, of which a repre- 



* Philippi, ill Wiegnian's Arcliiv. 184.'), pi. 1S7, p. 7, f. 14. 



