CONCHOLOGY. 



87 



larger ; suboval, compressed, and striated longitudi- 

 nally on the longer side from the aperture; mouth small, 

 orbicular ; length one line. 



Test Min. liar. tab. 1, fig. 2. 

 Found by Mr Boys at Sandwich and Reculver. 



2. Perforata Shell semilunar, perforated ; colour 

 white, opake, glossy. 



Test Min. liar. tab. 1, fig. 3. 

 Found at Sandwich and Cornwall. Probably a mu- 

 tilated specimen of the preceding. 



3. Intorta. Shell oval, compressed, opake, glossy, 

 composed of three and sometimes four compartments, 

 inner ones small ; wrinkled transversely ; aperture 

 •compressed semilunar ; diameter one-tenth of an inch. 



Test. Min. Rar, tab. 1, fig. 1. 

 On the British shores frequent. 



4. Subrotunda. Shell sub-orbicular, sub-compressed, 



smooth, glossy, opake; chambers three, the middle one Univalves' 

 elevated above the others on the upper side, but not vi- -—-y"^^ 

 sible beneath ; mouth small, angulated ; margin in live 

 shells yellow^ ; diameter about half a line. 

 Test: Min. Rar. tab. 1, fig. 4. 



Found among small sand, on the English shores com- 

 mon. 



5. Oblonga. Shell oblong, compressed, opake, glos- Oblonga. 

 sy, white ; on one side, the shell is divided into two 

 parts by a single longitudinal suture; on the other side, 

 the middle compartment is surrounded with a faint de- 

 pression, that separates it from the exterior one, and is 

 more elevated ; mouth a little produced, oval, margin 

 yellow ; length not half a line. 

 Test. Brit. tab. 14, fig. 9. 



In sand from Salcomb Bay, Devonshire. 



ORDER II. BIVALVES. 



Bivalves. ' his order of testaceous bodies was invented by A- 

 ^-~y-«- ristotle, and has been adopted by succeeding concholo- 

 gists. It consists of an assemblage of shells which are 

 composed of two concave plates, united laterally to each 

 other by means of a hinge. The genera may be conve- 

 niently arranged in two divisions, depending on the 

 form of the hinge. Other characters might be employ- 

 ed in the formation of subsidiary Sections and Families. 

 For instance, the circumstance of the valves being clo- 

 sed or gaping ; the shells equilateral or inequilateral, 

 equivalved or inequivalved. The internal or external 

 insertion of the cartilage of the hinge ought to be close- 

 ly attended to in a general arrangement; but at present 

 we choose to employ such characters as helps merely, in 

 the distribution of species. 



DIVISION I. DENTATED. 



Demated. This Division comprehends such shells as are furnish- 

 ed with teeth at the hinge. These teeth vary in num- 

 ber, form, and position, in the different species, and are 

 employed as marks in the construction of" the genera. 



Genus XXVI. Mya. 



''■VI. Shell generally gaping at one end, and furnished with 



A ' strong, broad, thick teeth at the hinge, not inserted into 



the opposite valve. 



A. Valves Gaping. 



3lypyme. ** Glycymeris. Shell oblong, thick, transversely 

 wrinkled, and gaping at both ends; hinge furnished 

 with a thick primary tooth, and a smaller one, besides 

 a series of wrinkles. Length five inches, breadth nine 

 or ten. 



Brit. Shells, tab. 142. 



This species is scarcely admissible into a list of Bri- 

 tish shells. It was introduced by Mr Donovan, merely 

 from the circumstance of its occurring in deep water 

 between the Dogger-bank and the eastern coast of Eng- 

 land, and likewise from its being acknowledged as Bri- 

 tish by some English collectors. 



2. Pholadia. Shell thin, opake, of an oval shape, 

 holadia, marked with fine concentric striae ; beak small, promi- 

 nent, and placed at one end ; valves, when shut, have 

 a large oval gape in front ; hinge furnished with a small 

 plate projecting inwards. 



Brit. Zool. tab. 44. fig. IQ. Bivalves. 



First noticed from Weymouth by Pennant. Found — - y-**' 

 on the Dorset coast by Dr Pulteney also, and on the 

 Devonshire coast by Mr Montagu. 



3. Arenaria. Shell oval, moderately concave, rough, Arenaria 

 with concentric striae ; beaks prominent ; hinge with 



one valve, furnished with a broad, thick, erect tooth, 

 by which it is joined to the toothless valve; the smaller 

 end gapes, and is reflected. Length two inches and an 

 half, breadth nearly four inches. 

 Brit. Zool. tab. +2. fig. 16. 

 At the mouth of rivers on the English and Scottish 

 shores, frequent. 



4. Truncata. Shell truncated at the smaller end Truncata, 

 where it gapes, and concentrically wrinkled; valves 

 concave and reflected at the smaller end ; tooth broad 



and erect. Length two inches or more, breadth about 

 three. 



Brit. Zool. tab. 41. fig. 14. 

 This species is found lodged under gravel at low wa- 

 ter mark, on various parts of the British shores. It is 

 the shell which Pennant should have referred to as the 

 one eaten by the Hebridians. In Orkney and Zetland 

 it is used as a supper dish when boiled, and is called 

 Smurslin. 



B. Valves Closed. 



5. Margaritifera. Shell ovate-oblong, sub-arcuated Margariti- 

 opposite the hinge, covered with a black epidermis, fera., 

 usually worn off at the beaks; a single tooth in one valve 



locks into a bifurcated tooth in the other. Length two 

 inches and a half, breadth five inches. 

 Brit. Zool. tab. 43. fig. 18. 

 This shell is found in several rivers of Britain. It 

 lives in those which are rapid, and which flow in moun- 

 tainous countries. It often produces pearls of a consi* 

 derable size, and of a good colour.. 



6. Ovalis. Shell strong, oval, of a dusky green co- _ ,. 

 lour, almost black at the smaller end ; beaks near the 

 larger end; hinge furnished with one tooth, which 

 locks into a bifurcated tooth in the opposite valve, these 



are strong and crenated ; there are likewise two lateral 

 laminae in one valve, and one in another. Length two 

 inches, breadth four inches. 



Brit. Shells, tab. 101. M. depressa. 



tab. 121; M. ovata. 



Found in England in slow running rivers. 



