M 



MOLLUSCA. 



[Arcacea. 



Inhabits the Mint, near Kendal. 



Rossmassler is wrong in supposing that this variety belongs 

 to the form Roissyi. 



I am indebted to the kindness of Miss Ellen T. Thomson, 

 of Stricklandgate, and Thomas Gough, Esq., surgeon, Kendal, 

 for specimens and a knowledge of this variety. 



Variety 4. Arcuata, pi. XXX,* f. 3. 



Shell small, subdepressed, thick ; hinge line considerably 

 arcuated; ligament prominent ; basal line greatly curved ; car- 

 dinal tooth in one valve very large ; lateral sinus arcuated, and 

 broad as it retires from the cardinal tooth; muscular impressions 

 deep. 



Found in the river Derwent, Bassenthwaite, Cumberland, a 

 little way below Ouse Bridge. 



Variety 5. Olivacea, pi. XXX,* f. 1. 



Small; substance of the shell thick, rather inflated; hinge line 

 nearly parallel; basal line with a flexure, and a very little arcu- 

 ated; valves with a slightly hollowed, longitudinal, gradually 

 widening furrow, from the umbones to the basal margin ; outer 

 surface olivaceous, with irregular, transverse furrows; umbones 

 much decorticated, which extends nearly to the dorsal extre- 

 mity of the valves ; inside of a dull flesh-colour, slightly nacred 

 towards the dorsal side; teeth small, distinctly tripartite in the 

 left valve, and very small and single in the other. 



This very curious variety was discovered by Thomas Glover, 

 Esq., of Smedley Hill, in the Leven, a little way below the lake 

 of Windermere, Westmoreland. 



Family II Arcacea. 



Shells provided with numerous small primary teeth, disposed 

 in a straight or interrupted line in each valve. 



Genus 4 Nucula. — Lamarck. 



Shell equivalve, inequilateral, transverse, oval, trigonal, or 

 oblong ; generally covered with an epidermis ; hinge linear, 

 narrow, divided into two parts by an oblique, produced, nearly 

 central pit, which is destined for the reception of the ligament, 

 the one anterior and the other posterior ; lateral teeth on each 

 side numerous, acute, elevated, somewhat recurved, those of 

 the opposite valve locking into the intervening spaces; umbones 

 contiguous, and not separated by an intervening area ; two 

 simple muscular impressions; mantle impression destitute of a 

 sinus. 



Section I. — Shells oblong-ovate. 



1. Nucula rostrata, pi. XXXIII, f. 16. 



Nucula rostrata, First Ed., pi. 25, f. 1G; Area rostrata, 

 Ency. Moth., pi. 309, f. 7, a, b ; Montagu, Sup., p. 55, pi. 27, 

 f. 7 ; Turton, Conch. Diet., p. 1 1 ; lb., Brit. Biv., p. 178 ; La- 

 marck, VI, pt. 1st, p. 58. 



Shell transversely oblong-ovate, somewhat convex, and rather 

 thin; smaller side produced into an arcuated, beak-like form, 

 which is provided with three transverse ribs; umbones nearly 

 central, approximate, somewhat inclined to the smaller side; 

 external surface pale horn-coloured, and a little glossy, with 

 strong, regular, undulating, diagonal stria;, which make an 

 abrupt, angulated turn across the ribs of the beak, terminating 



where the ribs of the beak commence ; these are crossed by 

 extremely minute, irregular, transverse stria?, which, however, 

 can only be seen by the aid of a strong lens, and appear more 

 like the scratches of a file than striae; teeth strong, regular, and 

 angulated, those on each side of the hinge pit with their angular 

 sides turned towards it ; inside very glossy and white. Length 

 not quite half an inch ; breadth three-quarters. 



Found off St. Abb's Head, Frith of Forth, by Captain Las- 

 key ; and I met with an odd valve at Holy Island. 



2. Nucula minuta, pi. XXXIII, f. 18. 



Nacula minuta, First Ed., pi. 25, f. 18; Turton, Biv., p. 178; 

 Area minuta, Montagu, p. 140; Brown, W T ernerian Mem., II, 

 p. 512; Area caudata, Donovan, III, pi. 78; Area modiolus, 

 Walker, p. 23, f. 81. 



Shell transversely oblong-ovate ; anterior side produced into 

 an angulated, arcuated beak, which is square at the point ; 

 posterior side rounded ; umbones small, pointed, and turned 

 towards the anterior side, with a small spindle-shaped depres- 

 sion under them, reaching to the point of the beak, and being 

 indented, gives a reflexed appearance ; teeth numerous, sharp, 

 and prominent ; external surface yellowish or pale olive-green, 

 covered with fine, distant, regular, transverse striae, and three 

 or four concentric ridges, according to the age of the shell ; 

 inside smooth, glossy, and of a bluish-white or pale purple ; 

 margin plain. Length three-eighths of an inch; breadth some- 

 what more than half an inch. 



Found at Sandwich; Tenby; Dublin Bay and Portmarnock, 

 Ireland ; and Frith of Forth, Scotland. 



3. Nucula oblonga, pi. XXXIII, f. 17. 

 Nucula obsoleta, First Ed., pi. 25, f. 17- 



Shell oblong-ovate; anterior side produced into a straight, 

 but slightly narrowed beak, with two shallow furrows running 

 from the apex to the point, which is slightly rounded ; posterior 

 side rounded; umbones straight, very blunt, and placed near 

 the posterior side ; exterior surface of a dark olive-green, with 

 nearly obsolete, transverse stria?; teeth strong, regular, promi- 

 nent, and triangular ; cartilage cavity spoon-shaped, and sloping 

 downwards ; inside smooth, and white ; muscular impressions 

 large ; a slight groove emanating below the umbones, termi- 

 nates on the margin at the beaked side. Length upwards of 

 half an inch; breadth upwards of seven-eighths. 



Discovered by Stewart Ker, Esq., at Greenock, and on the 

 beach of the opposite shore, where it is not uncommon. 



4. Nucula truncata, pi. XXXIII, f. 19- 

 Nucula truncata, First Ed., pi. 25, f. 19- 



Shell ovate, somewhat beaked at its anterior side above, with 

 an oblique truncation below the projecting point ; umbones 

 rather prominent, rounded, and nearly central; outside of a 

 dark olive-green, beset with numerous, extremely fine, close, 

 considerably undulated, transverse striae, and with exceedingly 

 fine, minute, longitudinal stria?, which can only be seen by the 

 aid of a lens; inside smooth, white; hinge with about thirty 

 sharp, elevated, and somewhat imbricated teeth; cartilage socket 

 nearly round, sloping downwards, and almost concealed below 

 the umbones. Length not quite half an inch; breadth about 

 three-quarters. 



Discovered by Stewart Ker, Esq., at Greenock, and near 

 Ardencaple, where it is not uncommon. 



