108 
Section I1.—Lateral teeth striated ; the shell strong. 
4, Macrra souipa, pl. XLI, f. 3, 4. 
Mactra solida, First Ed., pl. 15, f. 3,4; Montagu, p. 92; 
Donovan, II, pl. 61 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 white, 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 
Treland ; it lurks a few inches below the surface. 
5. Mactra truncata, pl. XLI, f. 5. 
Mactra truncata, First E:d., pl. 15, f.5; Montagu, Sup.,, p. 
34; Turton, Biv., p.68; Fleming, p. 427; Mactra subtruncata, 
Donoyan, IV, pl. 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 pallial 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. Macrra sustruncata, pl. XLI, f. 7. 
Mactra subtruncata, First Ed., pl. 15, f. 7; Montagu, p. 93; 
Ib., Sup., p. 34, pl. 27, f. 1; Turton, Biv., p. 70; Fleming, p. 
427; Forbes, p.48; Mactra Stultorwm, Pennant, pl. 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 stri, 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. Macrra striata, pl. XLI, f. 10. 
Mactra striata, First Ed., pl. 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 suboyate, its superior line gently arcuated, as 
well as the basal margin; surface brownish-yellow, covered with 
strong, transverse, equidistant strie; 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. 
MOLLUSCA. 
[Macrracga. 
I procured this species in Lough Strangford, County of 
Down, Ireland. 
8. Macrra Exuiptica, pl. XLI, f. 6. 
Mactra elliptica, First Ed. pl. 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 JZ. 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. Macrrina Triancuuaris, pl. XL, f. 25. 
Mactrina triangularis, First Ed., pl. 16, f. 25; Brown, 
Conch. Text Book, p. 140, pl. 18, f. 30; Goodallia triangularis, 
Turton, Biy., p. 77, pl. 6, f. 14; Fleming, p. 429; Forbes, p. 
48; Mactra triangularis, Montagu, p. 99, pl. 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. Macrrina minutissima, pl. XLII, f. 25, 26. 
Goodallia minutissima, Turton, Biv., p. 77, pl. 6, f. 155; 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. 
