92 



CONCHOLOGY. 



Nodosum, 



F.longatum, 



Exiguum, 



Medium 



Bivalves, tie produced ; epidermis yellowish-brown ; young shells 

 ^~~Y~~' are finely polished ; length two inches and a half ; 

 breadth two inches. 



Brit. Zool. tab. 51, fig. 40. 

 Found in several places on the coast. 



5. Nodosum. Shell rufous white, flat, sub-orbicular, 

 with twenty-four close set obtuse tubercles ; inside 

 white, glossy ; diameter three quarters of an inch. 



Test. Brit. p. 91. 

 Discovered in Falmouth, in Cornwall, by Mr Mon- 

 tagu. 



6. Elongatnm. Shell compressed, suboval, subangu- 

 lated, with" twenty-one ribs faintly wrinkled and round- 

 ed ; posterior side somewhat elongated and angulated ; 

 diameter a quarter of an inch. 



Test. Brit, page 82. 

 Found by Mr Montagu by dredging in Salcomb-bay. 



7. Exiguum. Shell convex, sub-triangular, with twen- 

 ty tuberculated ribs, the interstices strongly striated 

 transversely ; length about half an inch. 



Brit. Shells, tab. 82, fig. 3. 

 Found by Mr Montagu in Cornwall and Devon ; Mr 

 Boys has found it at' Sandwich ; Mr Laskey found it at 

 Dunbar ; and we have it from Zetland. 



8. Medium. Shell sub-triangular, sub-cordated, with 

 about thirty-six smooth ribs ; truncated on one side, 

 and running into an angle at the front margin ; the 

 other side is shorter, and rounded ; primary teeth one 

 in each valve, which, with the lateral ones, are strong 

 and elevated; length about an inch. 



Brit. Shells, tab. 32, fig. 1. 

 First described as British by Mr Montagu, whose 

 specimen was found at Hartlepool, on the coast of Dur- 

 ham. 



9. Rubrum. Shell smooth, red, glossy, pellucid, con- 

 vex ; hinge not quite central ; rounded at both ends ; 

 beak prominent ; hinge With nearly obsolete primary 

 teeth, lateral ones very conspicuous; diameter about 

 the eighth of an inch. 



Test. Brit. tab. 27, fig. 4. 

 Found by Mr Montagu on the coast of Devon, and 

 at Dunbar by Mr Laskey. 



10. Discors. Shell convex, sub-orbicular, glossy, 

 white, finely striated in an oblique direction, the striae 

 curved at the anterior side, the posterior end in a con- 

 trary direction, forming an acute angle with the others; 

 beak small, central, turning a little to one side ; size of 

 a pea. 



Test. Brit, page 84. 

 Found by Mr Montagu at Falmouth. 



11. Muricatidum. Shell white, opake, heart-shaped, 

 with a muricated margin ; minute. 



Test. Min. Ear. fig. 84. 

 Found at Sheppy island. 



12. Arcuatum. Shell thin, fragile, semi-pellucid, or- 

 bicular, white, finely striated transversely in an arcua- 

 ted manner, with a few concentric wrinkles ; beak cen- 

 tral, pointed at the apex, and turned to one side ; hinge, 

 with one primary tooth in each valve ; laminated teeth 

 remote ; diameter about half an inch. 



Test. Brit. tab. 3, fig. 2. 

 Dredged up in Falmouth harbour by Mr Montagu. 



13. Edcntula. Shell sub-ovate, thin, rounded at one 

 end, and sub-angulated at the other, with a few broad, 

 distant, concentric elevations and longitudinal stria?; 

 beak small pointed; hinge destitute of any primary 

 tooth; length two inches and a half; breadth three 

 inches. 



Brit. Shells, tab. 161, Maclra radio.'.a. 



F.ubrum, 



Dis'Ors, 



Muricatu- 

 lum, 



Arcuatum 



Edcntula, 



Fascuturo, 



Found by Mr Laskey at Portsmouth after a storm. Bivalve*. 



14. Fasciatum. Shell sub-orbicular, sub-pellucid, with 

 about twenty seven smooth, glossy, flattened ribs, slight- 

 ly tuberculated at the shorter side ; coloured with three 

 or four brown bands ; length three-eighths of an inch. 

 Test. Brit. tab. 27, fig. 6. 



Found on the shores of Cornwall, Devon, Leith, and 

 Zetland. 



Genus XXXIII. Cyclas. 



Shell almost orbicular, or a little transverse, not in- XXXIII. 

 fleeted on the fore fart; the hinge with two or three Cycias. 

 teeth, and two lateral ones, compressed and rather re- 

 mote. 



Obs. This genus of Lamarck contains species which 

 chiefly inhabit rivers and pools. The British species 

 have been referred to the genus Cardium or Tellina. 

 Their smooth surface and uneven margin forbid their 

 insertion in the former, and the want cf the fold in the 

 anterior part of the shell, forbid their insertion in the 

 latter genus. The inhabitant bears a close resemblance 

 to the molluscous genus Tethys. The three species are 

 viviparous. 



1. Cornea. Shell thin,"pellucid, sub-orbicular, con- Cornea, 

 vex, marked with fine concentric stria; ; epidermis horn- 

 coloured ; beak central, obtuse ; hinge with the central 

 teeth very small ; the lateral laminated ones remote and 

 prominent; sometimes half an inch long, and three 

 quarters broad. 



Brit. Zool. tab. 49, fig. 36, Tellina cornea. 

 Brit. Shells, tab. 96. 

 'Test. Brit. p. 86, Cardium corneum. 

 A common British shell, found in slow rivers and 

 stagnant pools. 



2. Amnica. Shell thin, sub-pellucid, oblique, sub- Amnica, 

 oval, convex, sulcated transversely, and striated longi- 

 tudinally towards the front ; umbo placed nearest to 



one side ; hinge furnished with one central tooth, and 

 two lateral teeth on each side, in one valve, standing 

 parallel one within the other, the outer of which is 

 very small ; in the other valve two approximating pri- 

 mary teeth stand oblique, with one lateral tooth on 

 each side ; epidermis horn-coloured ; length three- 

 eighths of an inch ; breadth half an inch. 



Brit. Shells, tab. 63. fig. 2, Tellina rivalis, 

 First distinguished as British by Dr Maton. It is a 

 common British shell, inhabiting the same places as the 

 preceding, resembling the above in shape. 



3. Lacustris. Shell sub-rhomboidal, thin, pellucid, Lacustris. 

 smooth, of a pale horn-colour, rather compressed round 



the margin ; umbo central, small, but extremely pro- 

 minent, giving a cordiform appearance to the lateral 

 aspect of the shell ; in each valve a primary tooth, one 

 of which is plain, the other bifid ; length three-tenths 

 of an inch. 



Test. Brit, page 89, Cardium lacustre. 

 First observed as British by Mr Swainson, in a river 

 near Bulstrode ; and since, in several places in England 

 by Mr Montagu. 



Genus XXXIV. Mactra. 



Shell cquivalve, inequilateral, transverse, a little gaping 

 at the sides ; the hinge tooth complicated, with an adja- 

 cent little pit ; the lateral teeth remote, compressed, and 

 inserted ; ligament interned, inserted in the pit of thr 

 hinge. 



XXXIV. 

 Mactra. 



