ACEPIIALA TESTACEA. 



373 



Nucula, Lam. — 

 lias the teeth of the hinge in a broken line. The form of the shell is elongated and narrowed towards 

 the posterior end. We do not know the animal, but it is probably not much unlike that of the pre- 

 ceding genus. 



For a long time we have placed here the Triyonice, Brug., so remarkable for their hinge, which is 

 furnished with two plates en chevron, crenulated on both surfaces, and each penetrating into two 

 cavities, or rather between four plates of the opposite side, similarly crenulated on their internal sur- 

 faces. From the marks on the inside of the valves we inferred that the animal had not tubes, of any 

 length at least; and MM. Quoi and Gaymard having discovered it alive, we find, in fact, that, like 

 the Arcaceae, it has an open cloak without any separate orifices, not even one for the anus. Its foot 

 is large, truncate, and hooked at its anterior part. The recent Trigonia resemble the Cockles in the 

 figure of their shell, and in the manner in which it is ribbed. Their interior is nacred. The fossil 

 Trigonia; are considerably different. Their shell is flattened on one side, oblique, longest in the direc- 

 tion perpendicular to the hinge, and crossed in the contrary direction by series of tubercles. 



THE SECOND FAMILY OF THE ACEPIIALA TESTACEA,— 



The Mytilace.*:, — 



Has the cloak open in front, but with a separate aperture for the passage of excrements. All of then; 

 have a foot with which tbey crawl, or at least draw out, direct, and fix the byssus. They are known 

 to the vulgar by the name of Mussels. 



Mi ssels, properly so called {Myfilus, Linn.), — 



Have a closed, triangular shell, with equal ventricose valves. One of the sides of the acute angle fornix 

 the hinge, and is furnished with a long, narrow ligament. The head of the animal is in the acute 

 angle ; the other side of the shell, which is the longest, is the anterior one, and allows the passage "t 

 the byssus; it terminates in a rounded angle, and the third side ascends towards the hinge, to which 

 it is joined by an obtuse angle; near this is the anus, opposite which the cloak forms a peculiar aper- 

 ture or little tube. The animal (Calli/ric/ie, Poli) has the edge of its cloak provided with branched 

 tentacula near the rounded angle, as it is there that the water required for respiration enters. In front, 

 near the acute angle, there is a small transverse muscle, and a large one behind near the ohtuse angle. 

 The foot resembles a tongue. 



In Mi/liliis, Lam., the summits [of the valves] are nearly terminal. Some species are smooth, others Striated. 

 The common Mussel \JU. edulis, I, inn.) is spread in extraordinary abundance along all our coast, where it is often 

 suspended, in Ions clusters, to rocks, piles, ships, &c. It forms an article of food of some importance, hut it is 

 dangerous when eaten to excess; [and under certain unknown circumstances, or to some individuals, bfltomes 

 deleterious]. Some species have been found in a fossil state, (which Brongaiart distinguishes geaerkwfl) bj the 

 name Mitiloide). 



In Modiolus, Lam., the apices are lower, and towards the third of the hins;e ; they are also more protuberant and 

 rounded, whence the shell has more of the ordinary shape of bivalves, We may also distinguish separately the 

 l.iihiiiinmiiK, Cut., which has an oblong shell, almosi equally rounded at both ends, and the summits Ten M, ' ;ir 

 the ant. -nor. They at first suspend themselves to stones, like the common Mussels, but then they perforate them, 



atid bury themselves 111 the excavations, whence they cannot again issue. After they have made their Cells, 



byssus ceases to grow.* One species (Mytilui lithqphagus, Linn.) is very common in the Mediterranean, where 

 it furnishes a food agreeable enough on account of its peppery taste. There is another [Modiola caudigera) which 

 has the posterior end of each valve armed with a vers hard little appendage, that it, perhaps, of service in the 1 

 ration of its dwelling^ 



Tin: I'm -11 w'aieu Minskis (Attodmtet, Brag.) — 

 Have the anterior angle rounded like the posterior ; and the angle near the anus obtuse, and ai 

 rectilinear: their thin and moderately ventricose shell has no tooth in the hinge, but merely a liga- 

 ment Occupying its entire length. The animal l.iiiiiiaa, Poti) is without B byssus ; and it creeps our 



• "We ■JPJfMl imacmr." .^,. .S,,wrrhr. ■■ that |U| remark MM 

 • on actual ob.rn ation, DtCMUC Wt bellrvr it !• 

 trarr to Ihr nature of the animal to be nt our ttmr attached hv ft 

 byatua, and not it another ; ai 



in length, in a. t-oni 

 pletcljr.fom lis u the fall .-norm." — Kn. 



t The mi'im bjr which the HU -a prrfrale 



rOCKI I. a. (t»< ' ' 



tlir wok li> I a art. on of the \ aire. ; ..' I. r« attribute It 



■■a bv the animal. All t ' 



. in the »,v 

 :ac. 



