CONCHIFERA. 
233 
Cardita margaritacea. Sowerby, III. p. 175. pi. 20, fig. 1. 
Transversely obovate, somewhat heart-shaped, and gibbose; 
anterior side a little produced, very short posteriorly, with an 
obscure longitudinal keel, and several narrow ridges, concen¬ 
trically undulated. 
The London Clay, Pegwell Bay. 
17. Pifo l a do> i ya simplex.—T he Simple Pholadomya, pL 
XCV. fig. 12. 
P. simplex. Phillips, Geo. York, I. pi. 4, fig. 31. 
Obliquely oblong-ovate ; a ridge extending from the beak to 
the base; surface smooth, with narrow concentric lines of 
growth, which form an acute angle on the ridge; beaks 
rather produced. 
The Calcareous Grit, Gristhorpe, Yorkshire. 
18. Pholadomya obliquata. —The Oblique Pholadomya, 
pi. XCVI. fig. 3. 
P. obliquata. Phillips, Geo. York, I. pi. 13, fig. 15. 
Obliquely transvorsely elongated ; posterior side very short; 
beaks placed quite to that side, aud much incurved ; anterior 
very large and dilated, a little compressed towards the margin ; 
surface with nearly equidistant concentric groovos and very fiat 
ribs. 
The Great Oolite, Brandsby, and the Lhi3, Bilsdale. 
19. Pholadomya acuticosta. —The Acute Ribbed Phola¬ 
domya, pi. XCVI. fig. 1. 
P. acuticosta. Sowerby, YI. p. 88, pi. 546, figs. 1, 2. 
Transversely oblong-oval; beaks obtuse and much incurved ; 
anterior side short, with four or five keel-shaped, longitudinal, 
divergent ribs, and many gradually lessening ones from them 
to the posterior side, which is gradually narrowed; basal line 
nearly straight. 
20. Pholadomya jequalis. —Tho Equal Pholadomya, pi. 
XCVI. fig. 7. 
P. acqiialis. Sowerby, YI. p. 88, pi. 546, fig. 3. 
Transversely and regularly oval, equally rounded at both 
extremities, and straight; beaks obtuse, incurved, and approxi¬ 
mate; with from six to eight slightly elevated, equal, diver¬ 
gent ribs, passing from the beaks over the centre of each 
valve, and terminating on the margin; basal lino gently curved. 
The Portland Stone, Weymouth, Dorsetshire. - 
Family III.—PHOLADARTA. 
Shell bivalve, with accessory pieces to tho valves; gaping 
much anteriorly. 
Genus LXX.—PHOLAS.— Linnams. 
Shell transversely oblong, equivalve, greatly inequilateral, 
nearly tho whole species gaping at both ends, and most of 
them with tho opening very largo at the anterior end, and ex¬ 
tending along tho basal margin; in somo species, however, it 
is nearly closed by a testaceous, almost smooth, somewhat 
tubular prolongation of the valves; hinge in various species 
with an unequally 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, fiat, tooth-like testaceous 
process, projecting from the interior of the shell, immediately 
within the umbones; in some species this is expanded and 
spoonshaped ; anterior dorsal margin near the beaks reflected, 
close, and flattened down upon tho 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 tho reflected mar¬ 
gin over the beaks, and the other intermediate between the 
umbones and the posterior side; muscular impression with a 
large sinus in its narrow part, the impression being somewhat 
expanded near to the sinus. 
1. PnoLAS cylindricus. —The Cylindrical Pholas, pi. 
XCIY. figs. 1, 2. 
P. cylindricus. Sowerby, II. p. 88, pi. 198. 
Transversely elongated, slightly compressed, and nearly 
cylindrical; anterior side plain ; posterior side muricated and 
pointed, with a small sinus in the edge ; beaks concealed by a 
reflection of the edges of the back; surface transversely 
striated ; with many longituginal elevations, rising with flat 
spines, where they decussate the transverse elevations. 
The Red Crag, Walton, and tho Coral Crag, Sutton. 
2. Pholas compkessa, —The Compressed Pholas, pi. XCIY. 
figs. 3, 4. 
P. compressa. Sowerby, YI. p. 213, pi. 603. 
Transversely obovate compressed; sides almost equally 
rounded ; gaping at each extremity; along the middle of one 
valve is a longitudinal rounded ridge, with a corresponding 
furrow in the other ; surface with many sharp, concentric 
ridges, these aro decussated by eight or ten longitudinal ones 
on tho anterior side; whole surface with extremely minute 
longitudinal striae. 
TheKimmeridgo Clay, Shotovcr, Oxfordshire. 
3. Pholas prisca. —The Ancient Pholas, pi. XCIY. f. 25. 
P. priscus. Sowerby, YI. p. ] *>7, pi. 581. 
Oblong oval, anterior side very short and rounded, with a 
deep angular sinus in its edge, which is closed up in the adult 
shell; posterior side lengthened and truncated ; beaks covered 
by a heart-shaped accessory valve; in the middle of each 
valve a longitudinal band is formed by a series of scales. 
The Lower Greensand, Sandgate, Kent. 
4. Pholas Candida. —White Pholas, pi. XCIY. p. 23, 24. 
P. Candida. Brown, Ill. Rec. Couch. Brit. p. 115, pi. 48, 
figs. 6 to 10. 
1 ransversoly elongated ; anterior side pointed ; posteriorly 
rounded; umboual region covered by an elongated accessory 
plate; surface covered with wide-set longitudinal and trans¬ 
verse striie, prickly at the anterior side. 
The Red Crag, Walton, Wood. 
5. Pholas crispata. —The Crisped Pholas, pi. XCIY. figs. 
8, 19, 20. 
P. crispata. Brown, Ill. Rec. Conch. Brit. p. 114, pi. 48, 
figs. 1 to 5. 
3 A 
