376 



MOLLUSCA. 



Fig. 190.— AoodoD dipsat. 



the sand or mud by means of a large, com- 

 pressed, and nearly quadrangular foot. The 

 posterior end of the cloak is garnished "nith 

 many small tciitacula. The Anmluntcb li\e in 

 fresh waters. 



We have some native sppries; and of tlie largest 

 {Mytilus cygneuR, Linn.) the valves are used to skim 

 milk. From its insipidity, the animal is not edible. 



M. de Lamarck distinofuishes, under the name of 

 Iridina, an oblung: species, whose hinge is (granu- 

 lated its entire length. The rioak of the animal is 

 closed a little behind.* Thr Dij'^n.'; of L-ach is 

 founded on another species, uldcb has tlie angles 

 more decidedly marked, and a vestige of a tooth in 

 the hinge. 



The Umoxes (Unio, Brug.) — 

 Kesernhle the Anodontes in the shell and in the 

 animal, hut the hinge is more complicated. There 

 is a short cavity in tlie anterior part of the right valve, which receives a short plate or tooth from the 

 left one, and behind it is a lung plate, which is inserted between two others on the opposite side. 

 They also inhabit fresh water, jireferring running streams. Sometimes the anterior tootli is more or 

 less large and unequal, as in the Mya margaritifcra, Linn., whose pearls have been used in making 

 ornaments. At other times this tooth is laminated, as in Mya picforum, Linn., known to evci7 body 

 [frrjin its shells being used in holding water colours]. 



(A gi'cat number of species, remarkable for their size and figure, are found in the lakes and rivers of North 

 America. M^l. Say and. Barnes [and Lea] have described them, and have proposed some subgenera amonust them.) 

 i\L Delamarck distinguishes the //j/rm, with the angular productions of the hinge so decided tliat their shell is 

 almost triangular. And the Casialia, the shell of which, somewhat heart-shaped, is striated with rays ; and the 

 teeth and plates of the hinge are grooved across their longest diameter, which gives them a relationship with the 

 T'igon'ue. 



There ou^ht tn he placed near the Uniones some marine shells, which have a similar animal, and ver>' nearly the 

 same sort of hinge, but the summits of the valves are more swollen, and prominent ribs radiate from them to the 



margins. These are the Cardi/a, Brug. Their 

 shape is more or less oblong or cordate. In 

 some the shell gapes on the lower side. The 

 Cypricardia, Lam., are Cardit^ with the tooth 

 xmder the summit divided into two or three. 

 Their form is oblong, and their sides unequal. 

 RL de Blainville has again separated the Coral- 

 liophnga, whose shell is thin, and the lateral 

 lamina [of the hinge] so much obliterated that it 

 might induce us to approximate them to the 

 Fig. J91.— CarditQ eaiicuiata. Venus. One spccies is known, that burrows in 



masses of coral. 

 The Venericardia, Lam., difTer from the Cardita only because the posterior lamina of their hmge is more trans- 

 verse and shorter, thus making an advance to the Venus ; their form is almost round. It may be inferred from 

 the muscular impressions that their animal has also a resemblance to that of the Cardita and of the Unio. Both 

 of them approach the Cardia in general form and in the direction of their ribs. 



I suspect tliat tliis is also the place for the Crassatella, Lam. {Paph'ia, Roiss.}, which has sometimes been 

 approximated to Mactra, and at others to Venus. The hinge has two slightly-marked lateral teeth, and two very 

 strong middle ones, behind which, extending to both sides, is a triangular cavity for an internal ligament. The 

 valves become very thick with age, and the impression made by the margins of the cloak, leads to the belief that 

 there are no oxten.iilc tubes. 



THE THIRD FAMILY OF THE ACEPIIALA TESTACEA,— 

 The Camacea, — 



Has the cloak closed, hut perforated with three holes, through one of which the foot passes ; the 

 second furnishes an entrance and exit to the water required for respiration ; and the third is the vent ; 

 the two latter are not prolonged into tubes, as in the following famdy. 



• Nulwitlj-,iaLidinu the similarity i.f tl,c sliell, lridiii;i Joes nul tn.-lun): (o tlii= family, hut to tlic CarJi^icea.— F.d. 



