natural cavities untouched and in their own native state. 



On the nature and habits of this interesting class of ani- 

 mals much remains to be known. The difficulty of observing 

 their economy must tend to hinder the progress of this know- 

 ledge; but every fact discovered must lend its aid towards 

 the desired object. With this view, I beg to offer a few 

 remarks on the habits of the Gastrochae s na, as observed on 

 this coast. 'W *& ' iJ teniarp nodos ibriJ ^d mow 



The Gastrochae na Pholadia (ikfya dubia of Turton and 

 others, blended with the G. cuneiform is of Spengler, but 

 more properly the G. modiolina of Lamarck) is found 

 frequently on these shores. This shelled animal has been 

 stated by authors as living in the interior of rocks and stones, 

 in the same manner as the Pholades and Saxicavae. Cuvier, 

 Lamarck, and others, however, denote it as inhabiting ma- 

 drepores and corals. The first two are not agreed as to the 

 position of the tubes in the body of the animal. The exa- 

 mination of the shells in question would lead me to conclude, 

 with Cuvier, that the tubes proceed from the upper or poste- 

 rior end of the animal as it lies in its cavity, and issue out 

 when the valves are open, as is the case in the Sblenes and 

 Mydd. These authors do not mention any case or envelope 

 surrounding the shell. Turton, in his Conchylia, represents 

 this animal as " living in the interior of rocks and stones 

 covered by the sea, where it forms an outer testaceous coat 

 in which the shell itself is embedded, surrounded by a slimy 

 mucus ; and this outer coat, or case, which is formed on the 

 inner surface of the decomposed rock, is quite smooth," 1 In 

 a country destitute of limestone, or soft rocks, these animals 

 are indebted to other means for supplying them with a habit- 

 ation. The G. Pholadia accommodates itself to crevices, not 

 the interior of rocks, where 1 ™ ^^nW^ft^Te^^^fl^cXywring 

 its shell, as here exhibited. (Jig. 52.) It is found among 

 madrepores and shelly fragments, thrown up with alluvial 

 sand and rubbish on the sides oPfo£ft§. B1B TOf£ £fi^£%&8 

 shown are composed of broken shells and gravel, mixed with 

 fragments of felspar, hornblende, and sand, strongly agglu- 

 tinated together : these are frequently intermixed with Ser- 

 pulae, particularly the S. seminulum. The inside is smooth, 

 and consists of thin layers of the calcareous secretion applied 

 by the animal in the formation of this chamber, which sonse- 

 \vhat resembles a flask ; the lengthened neck, through which 

 the animal passes its double tube, is formed of concentric 

 layers of the same substance, preserving, to a certain- depth, 

 the same figure as at the summit of it. riI ^°^ 9 * T 4'J3\pui 



D D 2 



