Bivalves. 



Minuta, 



Jt'istrata, 



Tenuis. 



XLI. 



Arca. 



Lactea, 



Fusca, 



XLII. 

 Pectun- 



W'LUS. 



numerous fine regular pectinated teeth j margin finely 

 crenated ; length three-eighths of an inch ; breadth 

 somewhat more. 



Brit. Shells, tab. 63. Area nucleus. 



Found on the British shores from Zetland to Corn- 

 wall. 



2. Minuta. Shell somewhat oblong, the anterior 

 side running into an angulated beak cutoff at the point; 

 finely striated transversely interrupted by three or four 

 strong concentric ridges; umbo very small, beneath, 

 which is a smooth depression ; teeth numerous, angu- 

 lated ; a cavity under the apex destitute of teeth j mar- 

 gin plain ; length three-eighths of an inch ; breadth 

 about half an inch. 



Brit. Shells, tab. 78. Area caudata. 



Found by Mr Boys at Sandwich, and at Dunbar by 

 Mr Laskey ; it likewise occurs in Zetland. 



8. Roslrata. Shell sub-ovate, the smaller end produ- 

 ced into a lip, which is reflected or arcuated, the oppo- 

 site end rounded ; beak small, nearly central, a little 

 reclined ; pellucid, horn-coloured, glossy, wrought with 

 very fine regularly transverse stria ; margin plain ; 

 length half an inch ; breadth three quarters. 

 Test. Brit. tab. 27. fig. 7. 



Found by Mr Laskey in the Frith of Forth. 



4. Tenuis. Shell sub-cordate, smooth, white, cover- 

 ed with an olivaceous epidermis ; umbo very small ; 

 beaks slightly inflected and placed near one end ; in- 

 side smooth, white, and somewhat nacred ; margin thin 

 and entire, hinge pectinated with about fifteen elevated 

 teeth, six on one side and nine on the other, divided 

 by a small concave plate that projects inwards ; diame- 

 ter about a quarter of an inch. 



Genus XLI. Arca. 



Shell transverse, inequilateral, beaks distant ; hinge in 

 a straight line, plain at the ends, and furnished with a 

 row of transverse parallel mutually inserted teeth; liga- 

 ment exterior. 



1. Lactea. Shell rhomboidal, yellowish white, co- 

 vered with a brown pilous epidermis, under which it is 

 furnished with numerous fine close-set rib-like longitu- 

 dinal striae, with a few concentric wrinkles, giving the 

 shell a reticulated appearance; umba turned to one side; 

 margin crenulated. 



Brit. Zool. tab. 58. fig. 59- 

 Brit. Shells, tab. 135. 

 On the shores of England and Scotland ; not com- 

 mon. 



2. Noce. Shell sub-rhomboidal, the smaller end of 

 each valve turning inwards, forming a sharp angle, 

 giving the smaller end of the shell a sub-cordated ap- 

 pearance; umbo placed nearest to one side; apex promi- 

 nent, shell striated, reticulated ; colour rufous brown, 

 inside whitish, or tinged with brown ; breadth about 

 half an inch. 



Test. Brit. tab. 4. fig. 3. 3. 

 Found on the British shores, but not frequent. 



3. Fusca. Shell finely reticulated, of a purplish 

 brown colour, destitute of anv markings, 



Brit. Shells, tab. 158. fig. 34. 

 Found on the shores, of Cornwall by Mr Donovan, 

 in Devonshire by Mr Montagu, and at Dunbar by Mr 

 Laskey. 



GZNUS XLII. PfcCTUNCULUS. 



Shell rrbicular, sub-equilateral, hinge arched, andfur- 

 voi.. VII. TART I. 



CONCHOLOGY. 97 



nished tvith a row of oblique, mutually inserted teeth; li- Bivalves. 

 gament external. ^r^" 



xr.nr. 



Pecten. 



Maiimu? 



1 . Pilosus. Shell strong, orbicular, covered with a Pi'osus, 

 dark brown pilous epidermis, particularly about the 

 margin ; beneath this the shell is coloured with zig-zag 

 lines of chesnut ; faintly striated longitudinally, and 

 obsoletely wrinkled transversely ; inside white, mar- 

 gin crenated ; diameter two inches and a half or more. 



Brit. Zool. tab. 58, fig. 68. Arca glycymeris. 



Brit. Shells, tab. 37. 



Lin. Trans, vol. viii. tab. 3. fig. 3. 4. 

 Common to Cornwall and Zetland. In Orkney we 

 have observed vast quantities of them thrown ashore, 

 of a very large size. 



DIVISION II. TOOTHLESS. 



In this division a simple ligament connects the valves, 

 and the hinge is destitute of teeth which lock into one 

 another. It admits of a division into two Sections. 



SECTION I. INEQUIVALVE. 



The inequivalve shells are in general somewhat irre- 

 gular in their growth, and have one of the valves lar- 

 ger and more convex than the other. 



Genus XLIII. Pecten. 



Shell eared ; beals contiguous ; hinge without teeth ; 

 ligament internal, fixed to a triangular cardinal cavity. 



1 . Maximus. Shell with fourteen or fifteen ribs, lon- 

 gitudinally grooved, and wrought with very fine striae; 

 upper valve flat, with a •depression at the umbo; lower 

 valve convex; auricles striated, equal, rectangular; length 

 five inches, breadth six. 



Brit. Zool. tab. 59- %. 61. 

 Brit. Shell?, tab. 49. 

 Found on various parts of the British shores. 



2. Jacobceus. Shell with seventeen or eighteen very Jacobseus, 

 convex ribs, rounded and striated transversely; a smooth 

 whitish depression at the umbo; lower valve pure white; 

 auricles equal, rectangular, striated; length four inches, 

 breadth five. 



Brit. Zool. tab. 60. fig. 62. 

 First noticed as British by Pennant ; found in Dor- 

 set, Cornwall, and Yorkshire. 



3. Opercularis. Shell sub-orbicular, with about twen- 

 ty round transversely striated ribs ; colour reddish ; 

 auricles nearly similar ; diameter about two inches and 

 a half. 



Brit. Shells, tab. 12. Ostrea subrufus. 

 Brit. Zool. tab. 60. fig. 63. P. subrufus. 

 Common on the British shores. 



4. Varius. Shell with twenty-eight echinated ribs ; Varius, 

 colour various, clouded ; upper valve less convex than 



the other ; auricles very unequal ; the longest ear on 

 the superior valve much wrinkled, the other striated 

 sidewise ; beneath the long ear of the superior valve, 

 a few teeth like laminae ; length two inches and a quar- 

 ter. 



Brit. Zool. tab. 6l. fig. 64. 



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

 On the English shores frequent ; found in Orkney 

 by Mr Neil, and in the Frith of Forth by Mr Sime. 



5. Lincatus. Shell sub- orbicular, with eighteen nar- L ; neatus, 

 row ribs with a red line upon the ridge of each on 



the upper valve ; lower valve white ; auricles nearly 

 w 



Opercu- 

 laris 



