CONCHIFERA. 



233 



Cardita jnaiv/aritacea. Sowerby, III. p. 17"). pi. 29, fig. 1. 



Transversely obovato, somowliat lioart-sliaped, anil gibbose ; 

 anterior side a little produced, very short posteriorly, with an 

 obscure longitudinal keel, and several narrow ridgos, concen- 

 trically unilulated. 



Thp London Cla)', PcgwoU Bay. 



17. PiioL.vno.^iYA SIMPLEX. — The Simple Pholadomya, pi. 

 XCV. fig. 12. 



P. simplex. Phillips, Geo. York, I. pi. 4, fig. 31. 



Oblicjuely 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 transversely elongated ; posterior side very short ; 

 beaks placed quite to that side, and much incurved ; anterior 

 very large and dilated, a little compressed towards the margin ; 

 surface with nearly equidistant concentric grooves and very flat 

 ribs. 



The Groat Oolite, Brandsby.. and the Lias, Bilsdale. 



19. PrroLADOMYA ACUTicosTA. — The Acute Ribbed Phola- 

 domya, pi. XCVI. fig. 1. 



P. aeutieosta. Sowerby, VI. 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 ^qpalis. — The Equal Pholadomya, pi. 

 XCVI. fig. 7. 



P. aequalis. Sowerby, VI. p. 88, pi. 54fi, 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 line gently curved. 



The Portland Stone, 'Weymouth, Dorsetshire. 



Family III.— PHOLADARTA. 



Shell bivalve, with accessory pieces to the valves ; gaping 

 much anteriorly. 



Gencs LXX. — PHOLAS. — Linnwus. 



Shell transversely oblong, equivalve, greatly inequilateral, 

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

 them with tiio opening very largo at the anterior end, and ox- 

 tending along the basal margin ; in some 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 striso, 

 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. Hat, tooth-like testaceous 

 process, projecting from tlic inlorior of the shell, immediately 

 within the umbones ; in some species this is expanded and 

 spoonshapcd ; 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 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 CYLINDRICU.S. — The Cylindrical Pholas, pi. 

 XCIV. 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 the Coral Crag, Sutton. 



2. Pholas compressa. — The Compressed Pholas, pi. XCIV. 

 figs. 3, 4. 



P. compressa. Sowerby, VI. 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 are decussated by eight or ten longitudinal ones 

 on the anterior side ; whole surface with extremely minute 

 longitudinal stria'. 



TheKimmeridge Clay, Shotover, Oxfordshire. 



3. Pholas prlsca. — The Ancient Pholas. pi. XCIV. f. 25. 

 P. priscus. Sowerby, VI. p. 157, 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 bv a series of scales. 



The Lower Greensand, Sandgate, Kent. 



4. Pholas Candida. — AVhite Pholas, pi. XCIV. p. 23, 24. 

 P. Candida. Brown, III. Rec. Conch. Brit. p. 115, pi. 48, 



figs. 6 to 10. 



Transversely elongated ; anterior side pointed ; posteriorly 

 rounded ; umbonal region covered by an elongated accessory 

 plate ; surface covered with wide-set longitudinal and trans- 

 verso striie, prickly at the anterior side. 



The Red Cr.ig," Walton, Wood. 



5. Pholas cuispata. — The Crisped Pholas, pi. XCIV. figs. 

 8, 19, 20. 



P. crispata. Brown, III. Rec. Conch. Brit. p. 114, pi. 48, 

 figs. 1 to 5. 



3 A 



