Mytivacga.] 
Generally rather shorter and broader than the former two 
varieties, the anterior side less indented than the edulis, and 
much thinner and more transparent, both in the shell and epi- 
dermis, which is generally of a rich yellow, or amber, under 
which the shell is beautifully radiated with deep purple, or 
blue; inside very smooth and glossy, with the radiations very 
distinct ; the crenulations under the beaks small. 
This variety is much less common than the M. edulis, and is 
generally met with in the estuary of rivers. 
Variety 4. Sussaxatiuis, pl. XLV, f. 4, 5, 6, 7. 
Mytilus subsaxatilis, Williamson, Mag. Nat. Hist., VII, p. 
353, f. 48, a, b, c, d; Mytilus angulatus, Alder; Mytilus soli- 
tarius, Mark; Mytilus edulis, var. crassus, Brown, MSS. 
Shell strong, solid, very thick in proportion to its length; 
beaks considerably elongated ; hinge line straight, which is par- 
ticularly obvious in the young shell (f. 6); front seam, or union 
of the valves, undulous; colour of a grayish-blue; the epider- 
mis dull olive; young shells deep bistre-brown. 
Inhabits the coasts of Yorkshire, Durham, and Northumber- 
land. 
Mr. Williamson says this shell “is found in large pools left 
by the retiring tide, in groups of three or four together, firmly 
attached by their strong byssus to the under surface of large 
stones.” He considers it a distinct species, and says “the cha- 
racter of its habitat, combined with its peculiar solid form, give 
it as good a title to be styled a distinct species as, if not a 
better one than, that of the transparent shell of the M. pellu- 
cidus, or the small blunted form of the shell of WW. incurvatus, 
does these species respectively.” 
I first noticed this variety, in 1810, in company with my late 
valued friend Mr. Hancock, of Newcastle, at the mouth of the 
Tyne, below Tynemouth, adhering to stones left dry by the 
tide, in small groups; and recorded it as a mere variety of 
MH. edulis; not being able to detect any specific distinction 
in the animals. There can be but little doubt that the five 
forms enumerated are only permanent varieties of the same 
species. 
Variety 5. Incurvatus, pl. XXVII, f. 12. 
Mytilus incurvatus, Pennant, IV, p. 111, pl. 64, f.74; Mon- 
tagu, p. 160; Maton and Rackett, p. 106, pl. 3, f.7; Brown, 
Wernerian Mem., II, p. 515; Ib., Ency. Brit. VI, p. 423; 
Turton, Biv., p. 197; Fleming, Edin. Ency., VII, p. 99. 
Shell strong, opaque, broader at the base, in proportion to 
its length, than any of the preceding varieties; posterior side 
much incurvated; shell for the most part greatly inferior in size 
to the other varieties, although in some few instances we have 
found them an inch and a half in length. 
2. Mytitus crenatus, pl. XXIII, f. 1, 2. 
Mytilus crenatus, First Ed., pl. 31, f. 1, 2; Davies and 
Willcox, Ann. of Phil., August, 1825, p. 148; Ib., Zool. 
Journ., I, p. 584; Lamarck, VI, p. 120; Ency. Meth., pl. 217, 
£.'3. 
Shell oblong-ovate, subtrigonal, beaks rather obtuse; with 
strong, longitudinal, rounded ribs, producing a crenulated mar- 
gin; slightly wrinkled transversely; covered with an olive 
epidermis, beneath which the shell is of a reddish-violet colour; 
inside tinged with golden-yellow, transversely streaked with 
purple, bluish at the margins, and crenulated. Length nearly 
three inches; breadth an inch and a quarter. 
U 
MOLLUSCA. 
77 
This is an introduced species, having been brought from 
India, by the ship “ Wellesley,” in 1816; and has propagated in 
Portsmouth Harbour, where it is now completely naturalized. 
Genus 13—Mopio_a—Lamarck. 
Shell subtransverse, equivalve, regular, oblique; form oblong, 
somewhat wedge-shaped, and greatly inequilateral; anterior side 
very small, and obtuse; posterior side rounded, and close; an- 
terior margin slightly gaping, for the passage of the byssus, and 
forming, with the base, a line oblique to the dorsal one; beaks 
nearly lateral; outside covered with a strong, horny epidermis ; 
hinge without teeth; ligament elongated, and subinternal; two 
muscular impressions, the posterior one large, sublateral, elon- 
gated, and irregular, the anterior one small, and terminal; the 
pallial impression irregular, and destitute of a sinus. 
1. Mopiora papuana, pl. XXVII, f. 1, 2, 3, 4, 5, 6. 
Modiola papuana, First Ed., pl. 29, f. 1, 2, 3, 4,5, 6; La- 
marck, VI, p. 111; Leach, MSS., p. 11; Modiola vulgaris, 
Fleming, p. 412; Modiola modiolus, Turton, Biv., p. 199, pl. 
15, f. 3, young; Mytilus modiolus, Pennant, IV, p. 113, pl. 66, 
f. 77; Montagu, p. 163; Donovan, pl. 23. 
The young shell, pl. XX VII, f. 2, 5, 6. 
Mytilus curtus, Pennant, IV, p. 112, pl. 64, f. 76 4, young; 
Mytilus barbatus, Donovan, pl. 70; Montagu, p. 161. 
Shell strong, convex, rounded and prominent, transversely 
subovate, oblong; posterior side, or that close to the beak, 
extremely short, and slightly rounded; anterior side extremely 
long, and much rounded; basal line slightly concave; outside 
covered with a strong, thick, purplish-black or dark brown epi- 
dermis, and longitudinally wrinkled ; inside smooth, and white, 
exhibiting pearlaceous reflections in some specimens. Length 
at broadest side three inches; breadth six inches. 
The fine specimen from which our drawing was made, was 
dredged in the British Channel, and is in the cabinet of Wm. 
Nicol, Esq., Edinburgh; and I possess a specimen, measuring 
seven inches in length, and three inches and a quarter in 
breadth, which was caught by a fisherman’s line, near the Bell 
Rock, coast of Forfarshire. 
The young shell in its first stages is frequently of a pale 
yellowish-white, beautifully radiated with pink or chestnut- 
brown, with transverse streaks of the same colours; as exhi- 
bited in our figures 5 and 6. Ina more advanced stage, it is 
covered with a strong, chestnut epidermis, having the anterior 
side and base beset with long, unequal, straggling filamentary 
processes, which have been termed a beard. This beard is 
merely a prolongation of the epidermis, which drops off when 
the shell grows to about two inches. In this condition it is the 
M. barbatus of authors. 
Variety 1. Umpiricata, pl. XX VII, f. 3, 4. 
Mytilus umbilicatus, Pennant, p. 228, pl. 68; Donovan, pl. 
40; Montagu, p. 164. 
Shell with a deep, intorted, and wrinkled depression under 
the beak. 
This is merely an accidental, and by no means uncommon, 
variety of the shell. 
The Af. papuana is a deep water species, and is firmly fixed 
to the bottom by a byssus, composed of long silky filaments. 
