CONCHIFERA. 



Transversely sub-oval ; one side rounded, the anterior one 

 acuminated and folded back with a hollow behind ; a longi- 

 tudinal furrow emanates from behind the reflection, and ter- 

 minates on the margin ; posterior side nearly plain, or with a 

 few concentric wrinkles ; anteriorly with numerous thin un- 

 dulating, sharp-angled wrinkles, and longitudinal divergent 

 grooves, producing a reticulated appearance ; inside with a 

 large much curved tooth, below the umbonal region in both 

 valves. 



The Pleistocene Marine Formation, Houth, Ayr ; the Coral 

 Crag, Sutton ; the Red Crag, Walton ; and Mammiferous 

 Crag, Postdam. 



6. Pholas constricta. — The Constricted Pholas, pi. 

 XCIV. fig. 21. 



P. constricta. Phillips, Geo. York, I. pi. 2, fig. 17. 



Transversely elongated ; anteriorly short, rounded, and 

 truncated ; posteriorly constricted and acuminated ; a furrow 

 from the internal region to the base ; whole surface with longi- 

 tudinal ribs. 



The Gault, Speeton, Yorkshire. 



7. PiioLAs DACTYLUs. — Dato Pholas, pi. XCIV. fs. 11, 12. 

 P. dacli/liM. Brown, 111. Rec. Conch. Brit. p. 115, pi. 49, 



figs. 1, 2, 3. 



Greatly elongated transversely ; umbonal region placed much 

 to one side, reflected, with a series of cells externally, and 

 covered with two concentrically striated valves ; posterior to 

 them a long, spatuliform, accessorial valve ; surface anteriorly 

 rough, with waved ribs decussated by longitudinal stri» ; pos- 

 terior side smooth, with some shallow lines of growth. 



The Pleistocene Marine Formation, Ayr. 



8. Pholas recondita. — Recondite Pholas, pi. XCIV. f. 22. 

 P. recondita. Phillips, Geo. York, I. pi. 3, fig. 19. 

 Transversely ovate, rounded at both sides, an oblique, longi- 

 tudinal, nearly central furniw, transversely striated. 



The Coral Rag, Malton, Yorkshire. 



9. Pholas papyracea. — The Papyrus Pholas. 



P. papyracea. Brown, 111. Rec. Couch. Brit. p. 114, pi. 49, 

 figs. 4, C, 7, 9. 



Transversely ovate, anterior side ventricose and rounded, 

 closed when the valves are shut; posterior side acuminated, trun- 

 cated, and with an accessory ring ; each valve with an oblique, 

 longitudinal groove, with coarse and parallel striae beyond it ; 

 posterior half with closer set, slightly oblique, crenate ribs. 



The Coral Crag, Sutton. 



10. Pholas gigantea. — Gigantic Pholas, pi. XCV. fig. 1. 

 P.gigantea. Sowerby. Geo.Tr, 2d Ser. IV. p. 338, pi. 14,f. 1. 

 Transversely elongated; nearly cylindrical; anterior side 



short and rounded ; posterior side elongated and angular below ; 

 surface with oblique radiating furrows and ribs ; margin 

 crenated. 



The Gault, Folkstone and Lympne. 



Genus LXX.—GASTROCHjENA.—»Spe«g/er. 



Shell equivalve, inequilateral, somewhat wedge-shaped ; an- 

 terior side rounded, when viewed in front, and posteriorly 

 acuminated ; anterior side gaping widely, its aperture being 

 sub-ovate, and acute behind ; hinge marginal and linear, des- 

 titute of teeth, but in their stead a small laminated appendage, 

 emanating from the umbo, allied to the same tooth-like pro- 

 cess in the genus Pholas ; ligament external. 



This shell is enclosed in a testaceous, irregular, claviform 

 tube, situate at its broader extremity ; it is open and attenua- 

 ted anteriorly, with an oblong, bilobate aperture, which is 

 nearly sub-divided by a projecting septum, that does not quite 

 reach across the opening ; these serve for the passage of the 

 two tubes of the animal ; the posterior end of the tube is 

 closed. This club-shaped tube is found either within the perfor- 

 ated cavities of rocks, or in old shells or corals, the testaceous 

 tube always protruding beyond the surface. 



1. Gastroch^na contorta. — The Contorted Gastrochse- 

 na, pi. XCVI. figs. 22, 23, 24. 



G. contorta. Sowerby, VI. p. 50, pi. 526, fig. 2. 



Sheath club-shaped, bent nearly at a right angle, its aper- 

 ture divided by two opposite ridges ; valves ovate, elongated ; 

 surface with very fine stria?, the intervening lines wide, oval, 

 and pointed. 



In the London Clay, Barton. 



2. Gastroch^na tortdosa. — The Tortuous Gastrochsena, 

 pi. XCVI. figs. 29, 30. 



• G. tortuosa. Sowerby, IV. p. 49, pi. 526, fig. 1. 



Its longest diameter four times the united depth of both 

 valves, obliquely lanceolate, and twisted ; hinge line straight ; 

 surface nearly smootli. 



Inferior Oolite, Blue Wick, Robin Hood's Bay. 



3. Gastroch^na pholadea.' — The Pholas-like Gastro- 

 chajna, pi. XCVI. figs. 20, 21. 



G. pholadia. Brown, 111. Rec. Conch. Brit. p. 116, pi. 48, 

 figs. 13, 14. 



Transversely sub-ovate and wedge-shaped ; broadly and 

 widly gaping at the anterior side, from which it gradually de- 

 creases until it reaches the opposite extremity ; beaks rather 

 prominent and obtuse ; hinge with an obscure, laminar, trans- 

 verse tooth in both valves. 



The Coral Crag, Sutton. 



Family IV.— TUBICOLA. 



Animal contained in a testaceous sheath, distinct from its 

 valves, incrusted entirely or in part in the wall of this tube, 

 or projecting outwards. 



Genus LXXI.— TERIDINA.— iamarc^. 



Shell orbicular, and entirely external, equivalve, inecjuilater- 

 al ; umbones greatly incurved, and covered by a somewhat 

 quadrangular, accessory process, which seems to be fixed to 

 the valves in front of the beak, with a subulate process in 

 front, and gaping at both extremities ; anterior opening an- 

 gular at the back, and the posterior rounded in front ; tube 

 thick, fistulous, posterior extremity smaller, and open, and 

 nearly divided into two from an interior projection on both 

 sides, and provided with an operculum ; anterior termination 



