406 MOLLUSC A. 



LiTHODOMUS, CuV., 



In which the shell is oblong, and almost equally rounded at the 

 two ends, the summit being close to the anterior extremity. The 

 species of this subgenus at first simply attach themselves to stones 

 like the common Mytili; subsequently, however, they perforate 

 aud excavate them in order to form ceils, into which they enter, and 

 which they never quit afterwards. Once entered, their byssus ceases 

 to grow(l). 



One of them, the Mytilus lithophagus, L., Chemn., VIII, 

 Ixxxii, 729, 730, is very common in the Mediterranean, where 

 from its peppery taste it is esteemed as food. 



A second, Modiola caudigera, Encyc. pi. 221, f. 8, has a very 

 hard small appendage at the posterior extremity of each valve, 

 which perhaps enables it to excavate its habitation. 



Anodontea, Brug. 



The anterior angle rounded like the posterior, and that next to the 

 anus obtuse and almost rectilinear^ the hinge of the thin and mode- 

 rately convex shell has no appearance of a tooth whatever, being 

 merely furnished with a ligament which extends along the whole of 

 its length. The animal, LimnjEA, Poli, has no byssus; its foot, 

 which is very large, compressed and quadrangular, enables it to 

 crawl upon the sand or ooze. The posterior extremity of its mantle 

 is provided with numerous small tentacula. The Anodontes inhabit 

 fresh water. 



Several species are found in France, one of which Mytilus 

 cygneitSy L., Chemn., VIII, Ixxxv, 762, is common in ponds, 

 Sec, with oozy bottoms. Its light and thin shells are used for 



(1) M. Sowerby doubts this fact, which is, however, well attested by M. Poll 

 from ocular demonstration Test. Neap., II, p. 215. The pi. xxxii of the same 

 work, fig. 10, 11, 12, 13, also proves that the animal resembles that of a Mytilus, 

 and not that of a Pholas or a Petricola. 



The mode in which the Lithodomi, Pholades, Petricolae, and some other bivalves 

 perforate stones, has been the subject of mucli discussion; some of the disputants 

 holding it to be effected by the mechanical action of the valvesj and others sim- 

 ply by solution. See the Mem. of M. Fleuriau de Bellevue, Journ. de Phys., 

 an X, p. 345; Poli, Test. Neap., II, 215, and Edw. Osier, Phil. Trans, part III, 

 1826, p. 342. All thing's considered, the first of these opinions, whatever be the 

 difficulties it presents, seems to us to come nearest to the truth. 



