37 G 



MOLLUSCA. 



Tig. 190.— Anudon dip 



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

 pressed, and nearly quadrangular foot. The 

 posterior end of the cloak is garnished with 

 many small tentacula. The Anodontes live in 

 fresh waters. 



We have some native species ; and of tlie larg;est 

 (Mytilus cygneus, Linn.) the valves are used to skim 

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



M. de Lamarck distinguishes, under the name of 

 Iridina, an oblono: species, whose hinge is granu- 

 lated its entire length. The cloak of the animal is 

 closed a little behind.* Tlie Dipsas of Leach is 

 founded on another species, which has the angles 

 more decidedly marked, and a vestige of a tooth in 

 the hinge. 



The Uniones {Unto, Brug.) — 

 Resemble the Anodontes in the shell and in the 

 animal, but the hinge is more complicated. There 

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

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

 They also inhabit fresh water, preferring running streams. Sometimes the anterior tooth is more or 

 less large and unequal, as in the Mj/a margaritifera, Linn., whose pearls have been used in making 

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

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



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

 America. MM. Say and Barnes [and Lea] have described them, and have proposed some subgenera amongst them.) 

 M. Delamarck distinguishes the Hyria, with the angular productions of the hinge so decided that their shell is 

 almost triangular. And the Castalia, 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 

 Tfigoni<e. 



There ought to be placed near the Uniones some marine shells, which have a similar animal, and very 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 Cardita, Brug. Their 

 shape is more or less oblong or cordate. In 

 some the shell gapes on the lower side. The 

 Cypricardia, Lam., are Carditae with the tooth 

 under the summit divided into two or three. 

 Their form is oblong, and their sides unequal. 

 M. de Blainville has again separated the Coral- 

 Uophaga, whose shell is thin, and the lateral 

 lamina [of the hinge] so much obliterated that it 

 might induce us to appro.ximate them to the 

 Venus. One species is known, that burrows in 

 masses of coral. 

 The Venericardia, Lam., differ from the Cardita only because the posterior lamina of their hinge 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 that this is also the place for the Crassatella, Lam. {Paphia, 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 extensile tubes. 



THE THIRI) FAMILY OF THE ACEPHALA TESTACEA,— 



The Camacea, — 



lias the cloak closed, but 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 : 



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



Fig. 191.. 



Nulivitiibt.inding the similaritv ul the shell, Iridii 



Qt belong to this f»miiy, but to the Cardiacea. — Kd. 



