326 Dr. Maton's Description of 



thin, semitransparent substance, not unlike bladder in texture, 

 and soluble in nitrous acid. The young shells are attached to 

 it by their epidermis, which, in fact, seems to be merely a mem- 

 branous expansion of the same substance, and to take its origin 

 from it for the purpose of confining the animal during the for- 

 mation of the shell. In some species, the attachment of the 

 membrane is so loose, that it is thrown otf very soon after the 

 animal is set at liberty; but in others it remains firmly adhering 

 to the calcareous matter during life. Most Jluvi a tile shells retain 

 this covering more or less entire, and it is the case with all the 

 species hereunder described, in all their stages of growth. The 

 membrane by which the calcareous matter of the shell is se- 

 creted, or deposited, is of a very diflerent nature, and has a more 

 immediate connexion with the contained animal. 



1. Mya labiata. 

 Tab. XXIV. Fig. 1, 2, 3. 



Mya testa subovali, valvis occlusissimis, alterius margine 

 1 abii instar) prominente. 



Habitat in America australi, fluviatilis. 



Testa firma, transversim striata, epidermide viridi, leviore, dc- 

 ciduci, intus margaritaceo-polita, anterius subrostrata. Cardinis 

 dens alterius valva solidus, subcochleariformis, antrorsum por- 

 rectus, fovete triangulari valvse oppositae insertus. Margo hujus 

 (h regione cardinis) quasi truncatus, illius rotundatus, subtenuis.. 

 Umbones parum prominentes. 



I have not mentioned the size of Mi/ a labiata in the above de- 

 scription, not thinking myself warranted so to do, unless I had 

 seen a great number of specimens. Those from which the cha- 

 racters were taken are all of the same size, and about 1 inch in 



length. 



