108 



MOLLUSCA. 



[Mactracea. 



Section II. — Lateral teeth striated ; the shell strong. 



4. Mactra solida, pi. XLI, f. 3, 4. 



Mactra solida, First Ed., pi. 15, f. 3, 4 ; Montagu, p. 92 ; 

 Donovan, II, pi. Gl and 126; Turton, Biv., p. 67 ; Fleming, 

 p. 426. 



Shell subtriangular, strong; sides nearly equal; umbones 

 almost central; lateral teeth large, prominent, and striated; 

 surface while, or yellowish-white, with a few concentric ridges. 

 General length an inch and a half; breadth an inch and three- 

 quarters ; although it not unfrequently attains the size of our 

 figure. 



Not unfrequent on many of the sandy shores of Britain and 

 Ireland ; it lurks a few inches below the surface. 



5. Mactra truncata, pi. XLI, f. 5. 



Mactra truncata, First Ed., pi. 15, f . 5 ; Montagu, Sup., p. 

 34; Turton, Biv., p. 68; Fleming, p. 427; Mactra subtruncata, 

 Donovan, IV, pi. 126. 



Shell triangular, very strong, thick, and nearly smooth, but 

 with a few remote, transverse, nearly obsolete lines of growth ; 

 sides nearly equal, considerably flattened, and truncated ; um- 

 bones rather prominent ; colour yellowish-white. Ordinary 

 length an inch and a half; breadth an inch and three-quarters. 



Some Conchologists consider this as a mere modification of 

 M. solida, but we possess it from the smallest size to the 

 adult, and the same form is preserved in all its stages. It 

 differs also from the latter species in the pallia] sinus being 

 broader, and does not run so far into the shell ; it is invariably 

 stronger. 



Plentiful in the Frith of Forth, of a large size; and is not un- 

 frequently met with on many of the British and Irish coasts. 



6. Mactra subtruncata, pi. XLI, f. 7. 



Mactra subtruncata, First Ed., pi. 15, f. 7; Montagu, p. 93; 

 lb., Sup., p. 34, pi. 27, f. 1 ; Turton, Biv., p. 70 ; Fleming, p. 

 427 ; Forbes, p. 48 ; Mactra Stidtorum, Pennant, pi. 52, f. 42. 



Shell subtriangular, strong, moderately convex ; umbones 

 large, prominent, placed considerably to one side, and nearly 

 straight ; the shorter side rounded, the other produced, and a 

 little pointed ; the anterior side so much flattened below the 

 umbones, that it presents an elongated, cordiform shape, when 

 viewed straight in front ; external surface yellowish-white, with 

 pretty strong, transverse striae, and sometimes with inequidis- 

 tant, strongly marked lines of growth; inside smooth, yellowish- 

 white. Length rarely exceeding three-quarters of an inch ; 

 breadth an inch. 



Common on most sandy shores. 



7. Mactra striata, pi. XLI, f. 10. 



Mactra striata, First Ed., pi. 15, f. 10; Brown, Ency. Brit., 

 VI, p. 471. 



Shell transversely elongated, rather strong ; umbones small, 

 subcentral ; anterior side subdepressed, and rounded ; posterior 

 side elongated, and subovate, its superior line gently arcuated, as 

 well as the basal margin ; surface brownish-yellow, covered with 

 strong, transverse, equidistant stria? ; inside smooth, white. 



This species bears a strong similitude to M. subtruncata, but 

 differs in the posterior side being less acute, the umbones being 

 much smaller in proportion to the size of the shell, in the striae 

 assuming nearly the character of ribs, and in the shell being 

 considerably larger. 



I procured this species in Lough Strangford, County of 

 Down, Ireland. 



8. Mactra elliptica, pi. XLI, f. 6. 



Mactra elliptica, First Ed., pi. 15, f. 6; Forbes, p. 48. 



Shell transverse, rather thin, elliptical, or slightly subtrian- 

 gular ; sides nearly equilateral, and slightly rounded ; umbones 

 nearly central, very much depressed ; cardinal margin promi- 

 nent ; surface covered with a thin, yellowish-brown, glossy epi- 

 dermis, beneath which the shell is nearly smooth, or obsoletely 

 striated transversely, which, however, can only be seen by the 

 aid of a strong lens ; teeth similar to the other species of this 

 section, but much smaller in proportion to the size of the shell; 

 inside smooth, white, and glossy. 



This shell was mistaken for the young of M. solida, but its 

 more elliptical form, its epidermis, and thinness, at once distin- 

 guish it from that species ; which characters it preserves in all 

 stages of growth. 



Found frequently in the Frith of Forth, and can readily be 

 procured at Cramond Island, at low water. Forbes found it on 

 the north coast, Isle of Man. 



Genus 35. — Mactrina Brown. 



Shell subtriangular, equivalve, nearly equilateral ; umbones 

 nearly central ; left valve with a strong, central, triangular, 

 slightly bifid tooth, which locks into a corresponding pit in the 

 opposite valve ; on each side of which are triangular, transverse 

 pits, for the reception of two small, depressed, cardinal teeth in 

 the right valve; ligament external; two strong muscular impres- 

 sions in each valve ; pallial impression entire. 



1. Mactrina triangularis, pi. XL, f. 25. 



Mactrina triangularis, First Ed., pi. 16, f. 25 ; Brown, 

 Conch. Text Book, p. 140, pi. 18, f. 30; Goodallia triangtdaris, 

 Turton, Biv., p. 77, pi. 6, f. 14; Fleming, p. 429 ; Forbes, p. 

 48 ; Mactra triangtdaris, Montagu, p. 99, pi. 3, f. 5. 



Shell elongated, subtriangular, strong ; sides a little unequal ; 

 umbones prominent, obtuse ; white, subopaque, smooth ; hinge 

 with a large, bifid, central, strong, cardinal tooth, in one valve, 

 and a pit on each side; opposite valve with a triangular, central 

 pit, for the reception of the tooth in the other valve, and a 

 small tooth on each side of the pit, which lock into the cor- 

 responding pits ; inside rather dull white ; the margin strongly 

 crenated. Length one-eighth of an inch ; breadth somewhat 

 less. 



Found in sand at Falmouth Harbour ; Portmarnock, Ireland ; 

 and Dunbar, Scotland ; very rare ; and on the Manx coast, by 

 Professor Forbes. 



2. Mactrina minutissima, pi. XLII, f. 25, 26. 



Goodallia minutissima, Turton, Biv., p. 77, pi. 6, f. 15; Fle- 

 ming, p. 429 ; Forbes, p. 48 ; Mactra minutissima, Montagu, 

 Sup., p. 37. 



Shell rather strong, subtriangular, white, and almost smooth ; 

 umbones prominent, nearly central ; sides very flat ; basal mar- 

 gin nearly parallel, but gently rounded at each extremity; hinge 

 strong; two cardinal teeth in one valve, with an intermediate, 

 pretty large, central cavity for the reception of the large, cardi- 

 nal, triangular tooth with which the opposite valve is provided ; 

 inside smooth, glossy ; margin plain. Somewhat less than a 

 quarter of an inch in length. 



