3C0 



SlPHOSOPHORA.- 



-MOLLUSCA.- 



-VEXEniD.E. 



Sub-class L— SIPHOXOPHORA. 



Tm3 {^reat group is divided into two orders — I. 

 Venekacla, iu wliicli the siphons are in general more 



or less separate — II. Puoladacea, in which the siphons 

 are united. 



Order I.— VENERACEA. 



In tliis order tlie hinder margin of the mantle is fiir- 

 iiiahed with two more or less elongated siphons under 

 the posterior adductor muscle, which are to a greater 

 or less degree separated from each other, and provided 

 with a large fan-shaped muscle on each side, for the 

 purpose of retracting them into the shell when the 

 animal fears external danger. The gills are short, and 

 not produced into the canal of the siphon, and the foot 

 is generally lamellar or elongate. 



Family— VENERID.E. 



Tliis family, with which we begin, is a numerous 

 one, and is remarkable for the elegant forms and 

 varied colours of the shells of many of the species 

 which belong to it. The animals have a large, com- 

 pressed, tongue-shaped foot, by means of which they 

 crawl ; and short unequal siphons, united sometimes 

 for a considerable portion of their length. The shell 

 is regular, closed, or sometimes slightly gaping ; gene- 

 rally free, seldom burrowing ; suborbicular in shape 

 or oblong. The hinge has usually three diverging 

 cardi[irtl teeth in each valve, and the hinder lateral 

 tooth, when present, is compressed, and forms a part 

 of the margin of the shell; the ligament is external, 

 marginal. The muscular impressions are smooth and 

 polished, and the pallial line is sinuated. The animals 

 of this family are all marine, free, and possess con- 

 siderahle locomotive powers ; a few only burrowing in, 

 or perforating rocks. They are found in all parts of 

 the world, though there is not much known of their 

 habits. Some of them, however, are eaten by man in 

 dillerent parts of the world, and are even esteemed a 

 delicacy. Their taste, we are told, is stronger than tliat 

 of oysters, and one must be habituated to it, to relish it. 

 The Venus shell appears to have been held in honour 

 by the ancients, and dedicated to the Goddess of Love. 

 The shells of the Veneridce show little organic structure, 

 and tlieir texture is very hard, approaching the por- 

 cellauous univalves in densit}', and in the absence of 

 almost any trace of animal matter. The species are 

 very numerous, upwards of five hundred and fifty being 

 indicated or described in M. Deshayes' Catalogue of 

 the VcncridcB in the British Museum. They differ 

 amongst themselves considerably in form, number, and 

 structure of the teeth, the shape of the paUial impres- 

 sion, &c., so that for convenience sake they have been 

 formed into no fewer than sixteen genera. We will 

 only mention a few. 



Gr.Nus Artkmis. — This genus has an orbicular, 

 compressed shell, deeply luniilate under the beaks, and 

 the hinge is provided with three teeth in each valve. 



The sinus of the pallial impression is deep, oblique, 

 kiangular, and sharp-pointed. The surface of the 

 valves is usually concentrically grooved, and of a pale, 

 or even white colour. 



Genus CYTiiEitEA {Meretrix). — This genus has a 

 very solid, smooth, veritricose shell, of a more or less 

 transversely oblong, or ovate form, with three cardinal 

 teeth in the hinge in each valve, and a small conical 

 anterior tooth beneath the nearly obsolete lunule. The 

 hinder lateral tooth is always lightly crenulated or 

 striated, and the sinus of the pallial impression is 

 moderate, and angular posteriorly. The surface of the 

 valves is generally smooth and shining, and covered 

 with a fulvous epidermis. 



Genu.s Cuneus (il/cTOe). — This genus is remarkable 

 for the compressed, ovate-trigonal shell, having the area 

 of the lunule deeply excavated, and the margins of the 

 shell regularly toothed. 



Genus Trigona. — This genus has a triangular, 

 wedge-shaped shell, w'ith very prominent beaks, and 

 an indistinct lunule. The hinge is provided with three 

 and sometimes four cardinal teeth, and a small anterior 

 one. The hinder lateral tooth is torn and diWded; tlie 

 internal margin of the valves is entire, and the pallial 

 sinus rounded, short, and horizontal. The shells are 

 usually thin and gibbous, and are frequently covered 

 with a glassy-looking epidermis. 



Genus Dione. — This genus, as represented in Plate 

 10, fig. 1, by Dione Chioxe, has an ovate, transverse, 

 inequilateral shell, with the interior margins of the 

 valves often thickened. The hinge has three cardinal 

 teeth in each valve, and a small anterior tooth under 

 the lunule. Tlie hinder lateral tooth is simple, neither 

 torn nor striated ; and the pallial sinus is wide, deep, 

 and somewhat ovate. The shells are often inflated, 

 and their surface is either smoath, suloated, striated, or 

 lamellar. 



Genus Cihce. — This genus has an ovate, somewhat 

 triangular, solid shell, depressed at the beaks. Tlie 

 hinge has three cardinal teeth in each valve, and there 

 is scarcely an}' trace of a pallial sinus. The external 

 surface of the valves is smooth, or concentrically striated 

 or grooved. 



Genus Venus. — This genus, as now restricted, has 

 a thick, turgid, ovate shell, with a prominent ligament, 

 a distinct lunule, and a small, often oblique pallial 

 sinus. The hinge is thick, and possesses three teeth 

 in each valve, wdiioh are divaricate, and sometimes 

 bifid. The surface of the shell in this gemis is either 

 warty, or ornaraenlod with concentric ribs or stria; or 

 lamulla?, or thc-y are decussated by longitudinal furrows. 



Genus Mekcenaria. — This genus has a triangu- 



