Mytilacea.] 



MOLLUSCA. 



75 



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 subequivalve, compressed, somewhat distorted, and la- 

 mellar; hinge lateral, linear, marginal, and internally crenulated; 

 the crenulae 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. Crenatula Travisii, pi. 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 incurved ; 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, pi. XXIII, f. 12, 13, 14. 



Crenella elliptica, First Ed., pi. 31, f. 12, 13, 14 ; Jeffreys, 

 Mai. and Conch. Mag., No. II, p. 45 ; Brown, Conch. Text 

 Book, p. 143, pi. 18, f. 13; Mytilus decussatus, Montagu, Sup., 

 p. 69 ; Laskey, Wernerian Mem., I, p. 394, pi. 8, f. 17 ; Fle- 

 ming, Brit. An., p. 411. 



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 striae, and crossed by very minute, equidistant, con- 

 centric striae, 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. 



Family II — Mytilacea. 



Hinge with a linear, subinterior, marginal ligament, very 

 entire, and occupies a considerable portion of the anterior mar- 

 gin ; shells generally foliaceous. 



Genus 10. — Pinna. — Linnaeus. 



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, pi. XXVI, f. 1. 



Pinna ingens, First Ed., pi. 30, f. 1 ; Pennant, IV, p. 115 ; 

 Montagu, p. 180 and 583; lb., Sup., p. 72; Brown, Ency. Brit., 

 VI, p. 424; lb., Wernerian Mem., II, p. 516; Maton and 

 Rackett, p. 112; Turton, Biv., p. 221, pi. 20, f. 1; Pinna 

 fragiles, Turton, Biv., p. 222, pi. 20, f. 20 ; Fleming, p. 406 ; 

 Pinna Icevis, Donovan, pi. 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 laminae, or plates ; a few 

 interrupted, longitudinal striae rise from the beak, crossing the 

 wrinkles, and sometimes forming on the broader portions of 

 the shells, a few remote concave 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- 

 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 ; Salcomb 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, pi. XXVI, f. 3. 



Pinna pectinata, First Ed., pi. 30, f. 3 ; Pinna fragiles, 

 Pennant, p. 114, pi. 59, f. 80 ; Fleming, p. 406 ; Pinna pecti- 

 nata, Montagu, p. 178; Brown, Ency. Brit., VI, p. 424 ; Tur- 

 ton, Biv., p. 223, pi. 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 



