114 



MOLLUSCA. 



[Pholadaria. 



cular impressions, extending nearly all along the arch of the 

 cardinal margin ; pallial impression interrupted, but destitute of 

 a sinus ; ligament external, linear, expanded over the outer 

 surface of the cardinal facets ; cartilage situate in a small, 

 short, triangular pit, immediately under the umbones, which 

 are slightly prominent. 



1. Galeomma Turtoni, pi. XXIII, f. 15, 16. 



Galeomma Turtoni, First Ed., pi. 31, f. 15, 16; Turton, 

 Zool. Journ., II, p. 361, pi. 13, f. 1. 



Shell tumid in the middle, compressed towards the extre- 

 mities, which are rounded and closed ; with a large oval gap at 

 the basal margin; hinge destitute of teeth; of a dirty or cream- 

 white colour ; surface covered with close-set, irregular, trans- 

 verse, interrupted opaque lines ; umbones prominent. Length 

 two lines and a half; breadth not quite half an inch. 



Dredged in the English Channel, by Dr. Turton. 



Genus 47 Pholas Linnaeus. 



Shell transversely oblong, equivalve, greatly inequilateral ; 

 nearly the whole species gaping at both ends, and most of them 

 with the opening very large at the anterior end, and extending 

 along the basal margin ; in some species, however, it is nearly 

 closed by a testaceous, almost smooth, somewhat tubular pro- 

 longation of the valves ; hinge in various species with an une- 

 qually sized, small, recurved tooth in each valve; external 

 surface generally roughened with muricated striae, presenting a 

 rasp or file-like appearance ; most of the species provided with 

 a greater or lesser number of accessory valves, situate near the 

 fulcrum of the hinge, and connected with the shell only by the 

 epidermis, which passes over them; each valve furnished with a 

 long, curved, flat, tooth-like, testaceous process, projecting from 

 the interior of the shell, immediately within the umbones; in 

 some species this is expanded, and spoon-shaped; anterior dorsal 

 margin near the beaks reflected, close, and flattened down upon 

 the umbones in some species, and in others a second margin is 

 produced, situate remote from the first, with the intervening 

 space divided by a series of transverse septa; two principal 

 impressions, formed by the adductor muscle, one of which is 

 placed on the reflected margin over the beaks, and the other 

 intermediate, between the umbones and the posterior side; mus- 

 cular impression with a large sinus in its narrower part, the im- 

 pression being somewhat expanded near to the sinus. 



Section I. — Valves divided by a longitudinal groove. 



1. Pholas crispata, pi. XLVIII, f. 1,2, 3, 4, 5. 



Pholas crispata, First Ed., pi. 9, f. 1, 2, 3, 4, 5 ; Montagu, 

 p. 23; Donovan, II, pi. 62 ; lb., Pholas parvus, young shell, 

 pi. 69; Turton, Biv., p. 6 ; Fleming, p. 456; Forbes, p. 57. 



Shell strong, inflated, transversely subo.val, very open at both 

 sides; one side rounded ; the anterior one acutely beaked, at 

 which side the superior margins, from the umbonal region to 

 the extremity, are thickened, smooth, and reflected, with a 

 hollow behind ; from the internal end of such reflection ema- 

 nates a longitudinal, rather deep furrow, — varying in width in 

 different individuals, — and terminating on the basal margin; 

 posterior side nearly plain, with irregular, transverse, slight 

 wrinkles; anterior side with numerous, thin, undulating, con- 

 ■ nitric wrinkles, and longitudinal, divergent grooves, producing 



a reticulated appearance; inside smooth, white, and glossy, with 

 an elevated, longitudinal ridge, corresponding to the external 

 furrow ; below the umbonal region in both valves is a long, 

 flat, greatly curved, transverse tooth; external surface of a dull, 

 opaque yellowish-white, sometimes of a ferruginous hue. 



Found on many of the British and Irish coasts, burrowing in 

 limestone or clay, its retreat being marked by a circular hole on 

 the surface. 



2. Pholas papyracea, pi. XLIX, f. 4, 6, 7, 9. 



Pholas papyracea, First Ed., pi. 8, f. 4, 6, 7, 9 ; Goodall, 

 MSS.; Turton, Biv., p. 2, pi. 1, f. 1, 2, 3, 4; Pholas lamellata, 

 Fleming, p. 456 ; Pholadidea Loscombiana, Fleming, Conch. 

 Diet., p. 147. 



Shell semiclavate ; anterior side ventricose, and very obtuse, 

 somewhat rounded, and closed when the valves are shut, 

 and quite smooth for about half of its surface ; open and 

 truncate at the posterior and smaller side, which is provided 

 with a produced accessorial ring, of a brownish papyraceous 

 appearance, and extending about three-eighths of an inch 

 beyond the truncated termination, its diameter increasing out- 

 wardly; the hinder half covered with close-set, slightly oblique, 

 crenate ribs; near the centre of each valve is a somewhat 

 oblique, longitudinal groove, beyond which they are covered 

 with coarser and more parallel striae ; inside dull white, with a 

 longitudinal rib corresponding with the external groove ; teeth 

 rather short, and compressed ; on the margin above there is an 

 erect, slightly triangular, somewhat concave plate, much larger 

 in one valve, and containing a portion of the animal fold, but 

 destitute of a permanent ligament. Length three-quarters of 

 an inch ; breadth eleven inches and three-quarters, including 

 the annular appendage. 



This ring is divisable into two equal and similar parts, the 

 segments being united by a thin elastic membrane ; the back 

 is provided with two accessorial appendages, with the margins 

 of the valves reflected at their anterior side, so as to form a 

 double obtuse keel, reaching as far as the longitudinal groove, 

 near the end of which is a kind of elevated joint, where the 

 accessorial valves are attached. 



3. Pholas lamellata, pi. XLIX, f. 10, 11. 

 Pholas lamellata, Turton, Biv., p. 4, pi. 1, f. 5, 6. 



Shell very open anteriorly, where the valves are depressed, 

 slightly reflected, and produced into a beaked termination, the 

 margins of both valves on this side being strongly serrated, and 

 nearly closed posteriorly; with an erect, laminar process on the 

 superior margin, over the umbonal region; valves with a nearly 

 central, longitudinal groove, emanating from the umbones, and 

 terminating on the base; whole surface covered with close-set, 

 somewhat obliquely transverse, crenate ribs, which become 

 coarser and straighter beyond the longitudinal groove ; inside 

 white, and smooth, with a longitudinal rib in the middle, cor- 

 responding to the external groove ; teeth long, compressed, and 

 slender, with a triangular process above them ; destitute of 

 accessorial valves. 



This species is nearly allied to, if not a variety of the pre- 

 ceding shell. It was introduced by Dr. Turton, who remarks, 

 " It has been suggested to us, that a belief is entertained of 

 this being the young of P. papyracea. But as we have oppor- 

 tunities of examining each of them in every stage of their 

 growth, both perfect and with the valves separated, we can with 



