MytILacka. | 
Shell smooth, or provided with a few scales near the margin, 
generally of a uniform, dull greenish-brown, with pale purple 
rays; beaks separated by a linear, transverse cavity; inside 
pearlaceous, and glossy, except round the margin, which is dull, 
and extremely thin; hinge with a single, small denticle, which 
fits into a slight hollow in the opposite valve. Length and 
breadth nearly equal. 
First discovered in Bantry Bay, by Miss Hutchins, and after- 
wards found by Dr. Turton in Dublin Bay. 
Genus 8.—CrENATULA.—Lamarck. 
Shell subequivalye, compressed, somewhat distorted, and la- 
mellar; hinge lateral, linear, marginal, and internally crenulated; 
the crenule placed in a continuous series along the hinge, each 
of them presenting a small rounded callosity, and excavated for 
the reception of part of the ligament; muscular impressions 
almost obsolete, of an oblong form, and situate near the ante- 
rior margin of the pearlaceous substance. 
1. Crenatuta Travis, pl. XXIII, f. 20. 
Crenatula Travisii, Turton, Mag. Nat. Hist., VII, p. 350, 
f. 47. 
“Shell rhombic, rounded below, transparent, whitish, with 
pale violet, longitudinal, interrupted stripes; the anterior mar- 
gin incuryed; nearly an inch long, and full half an inch broad ; 
extremely thin and brittle; obliquely truncate at the top, with 
a few pale violet spots below; hollowed out at the front margin 
in a slight crescent-shaped form.”— Turton. 
Taken alive at Scarborough, by Mr. Bean, and is in his 
cabinet. 
Genus 9.—CRENELLA.—Brown. 
Shell oblong-oval, equilateral, ventricose; beaks obtuse, 
slightly turned to one side; hinge destitute of teeth, but with 
a flattened, horizontal, slightly crenated plate on one side of 
the hinge in each valve; right valve with a triangular, horizon- 
tal, projecting, reflexed plate, and the left one with an oblique 
plait, both of which are a little crenated externally. 
1. CRENELLA ELLIPTICA, pl. XXIII, f. 12, 13, 14. 
Crenella sere First Ed. pl. 31, f. 12, 13, 44 P Settreys; 
Brown, Conch. Text 
Book, p. 143, pl. 18, f. 133 “Hytilus decussatus, Montagu, Sup., 
p- 69; Paskey, Wernerian Mem., I, p. 394, pl. 8, f. 17; Fle- 
ming, Brit. An., p. 411. /$a¥ 
Shell longitudinally ovate, ventricose, thin, and pellucid; 
umbones acute, turned to one side; sides equal, rounded ; 
covered with a pale olive-green epidermis; with fine, regular, 
divergent strie, and crossed by very minute, equidistant, con- 
centric striz, and a few distant lines of growth, producing a fine 
decussated appearance when seen under a strong lens; beneath 
the epidermis the shell is white; inside smooth, exhibiting 
nacred reflections, the margins finely crenulated. Length an 
eighth of an inch; breadth not so much. 
Discovered by Captain Laskey at Dunbar; I dredged it in 
the Frith of Forth, opposite Portobello; it has been also found 
at Zetland, and the coast of Argyle; and J. G. Jeffreys, Esq., 
met with it at Lerwick Sound, in 1841. 
MOLLUSCA. 75 
Famity II.—Myrivacea. 
Hinge with a linear, subinterior, marginal ligament, very 
entire, and occupies a considerable portion of the anterior mar- 
gin; shells generally foliaceous. 
Genus 10.—Pi1nna—Linneus. 
Shell equivalve, longitudinal, oblique, wedge-shaped; beaks 
forming an elongated point ; posterior side generally truncated, 
and always gaping; the base and anterior margin forming toge- 
ther a straight line, the latter gaping a little in the centre for 
the passage of the byssus; hinge without teeth; ligament mar- 
gin greatly lengthened and linear, and continuing along the 
whole dorsal region; two muscular impressions in each valve, 
the posterior one very large, almost central, the anterior one 
terminal, and sometimes double; pallial impression destitute of 
a sinus. 
1. Pinna INGENS, pl. XXVI, f. 1. 
Pinna ingens, First Ed., pl. 30, f. 1; Pennant, IV, p. 115; 
Montagu, p. 180 and 583; Ib., Sup., p. 72; Brown, Ency. Brit., 
VI, p. 424; Ib., Wernerian Mem., II, p. 516; Maton and 
Rackett, p. 112; Turton, Biv., p. 221, pl. 20, f. 1; 
fragiles, Turton, Biy., p. 222, pl. 20, f. 20; Fleming, 
Pinna levis, Donoyan, pl. 152. 
Shell nearly straight from the beak along the hinge line, 
slightly turned inwards at the apex, and connected the whole 
length, very rugged, foliaceous, with irregular, concentric wrin- 
kles emanating from the beak at the open side, and running 
lengthways, turn to the hinge at nearly right angles; some- 
times in the form of interrupted laminz, or plates; a few 
interrupted, longitudinal strie rise from the beak, crossing the 
wrinkles, and sometimes forming on the broader portions of 
the shells, a few remote concaye spines ; opposite side concave, 
or indented, swelling out gradually at the larger end, where 
the valves are always separated, leaving a gap between them; 
basal margin irregularly waved; external surface of an opaque, 
dull horn-colour, frequently inclining to umber-brown ; some- 
Pinna 
p- 406 ; 
times of a blue cast towards the smaller end; inside smooth, 
glossy, of a dark pearlaceous lustre, and a little lamellated 
towards the beak. 
This species grows to a large size, being not unfrequently 
upwards of twelve inches in length, and seven inches in breadth 
at the basal end. 
Found in the Hebrides; Saleomb Bay, Devonshire; and 
found at Portrush, County of Antrim, Ireland, by Mrs. Clew- 
low, of Belfast. They are found in gravelly bottoms, among 
mud, standing upright, the smaller end being downwards, and 
firmly attached to their habitat by a byssus of long silky fila- 
ments, of a dark purplish-brown colour, two or three inches in 
length. 
2. Pinna FRAGILIs, pl. XXVI, f. 3. 
Pinna pectinata, First Ed., pl. 30, f. 3; Pinna fragiles, 
Pennant, p. 114, pl. 59, f. 80; Fleming, p. 406; Pinna pecti- 
nata, Montagu, p. 178; Brown, Ency. Brit, VI, p. 424; Tur- 
ton, Biv., p. 223, pl. 19, f. 1. 
Shell subpellucid, thin, brittle, of a light horn-colour, some- 
times greenish, but darker towards the beaks; surface with 
about eleven longitudinal, narrow ribs, emanating from the 
apex, and extending to the basal margin, these are beset with 
