218 



CONCHIFERA. 



PsAMMOBlA. 



Genus XLIIL— ARCOPAGI A.— ZeacA. 



Shell thick, transverse, slightly iuequivalve, inequilateral ; 

 right valve suh-depressed ; beaks very small, nearly straight ; 

 with two primary teeth in both valves, each of the larger ones 

 cleft : left valve with two remote, lateral teeth, that on the 

 anterior side large, with a sinus betwixt it and the margin, 

 for the reception of the lateral tooth of the opposite valve, 

 muscular impressions large and deep ; pallial impression 

 interrupted by a broad, very large, tongue-shaped, oblique, 

 nearly central sinus, reaching two-thirds across the valves, both 

 defined by a broad, deep, irregular groove ; which passes 

 through the muscular impressions ; margin very broad and 

 glossy, as far as the pallial impressions ; ligament sub-external, 

 near the centre punctated. 



1. Arcopagia crassa. — Thick Arcopagia, pi. LXXXIX. 

 fig. 39. 



Tellina crassa. Turton, Brit. Bia. p. 109, pi. 7, f. 2, Arco- 

 paffia crassa, Brown, 111. Rec. Conch. Brit. p. 99, pi. 40, f. 8. 



Transversely sub-ovate, somewhat oblique and twisted, and 

 slightly unequal valved, the left one being the longer, and 

 considerably more convex than the other ; beaks short and 

 rather obtuse, and sub-central ; whole surface with pretty 

 regular, strong, concentric striae, which become wiiler as 

 they approach the base, with irregular lines of growth ; from 

 the beaks a well-marked furrow emanates, and terminates on 

 the margin. 



Mammiferous Crag, Postwick, and the Red Crag, Sutton. 



Sub-division III.— SOLENAIRES. 



Genus XLIV.—PSAMMOBIA.—Zawarc/t. 



Shell transverse, oblong, somewhat angular, gaping at each 

 extremity, and covered with a thin horny epidermis ; with two 

 short, bifid, cardinal teeth, in the left valve, and one in the 

 right; two distant, sub-orbicular, muscular impressions in both 

 valves, situate near each end of the valve ; pallial impressions 

 with a very large sinus ; ligament external, and supported 

 upon a prominent fulcrum. 



1. PsAMMOBiA rigidia. — The Rigid Psammobia, pi. 

 LXXXIII. fig. 1 6, and pi. LXXXIX. fig. 48. 



P. riffida. Sowerby, Sil. Syst. pt. II. p. 617, pi. 8, fig. 3. 



Considerably elongated transversely, its length not half its 

 width ; anterior side somewhat attenuated ; posterior side 

 truncated ; beaks obtuse, situate nearest the anterior side ; 

 base straight ; surface with from ten to twelve sharp trans- 

 verse ribs and furrows ; and three divergent ridges emanating 

 from the beaks and passing towards the base. 



The Lower Ludlow Rock, near Aymestry. 



2. Psammobia Ferroensis. — The Ferro Psammobia, pi. 

 LXXXIX. fig. 44. 



P. Ferroensis. Brown, 111. Rec. Conch. Brit. p. 101, pi. 

 40, figs. 1, 2. 



Transversely elongated, compressed ; anterior side obliquely 

 truncated, and with an elevated ridge running from the beaks 

 to the base ; posteriorly a little contracted and rounded ; sur- 

 face with strong transverse strife, which are angulated on the 

 truncations. 



The Coral Rag, Sutton. 



3. Psammobia vespebtina. — The Bat's-wing Psammobia, 

 pi. LXXXIX. fig. 54. 



P. vesperlina. Brown, 111. Rec. Conch. Brit. p. 102, pi. 

 29, figs. 30, 31. 



Transversely oblong ovate, both sides rounded ; beaks small, 

 nearly central ; surface with fine concentric strise. 



The Coral Crag, Ramshot. 



4. Psammobia solida. — The Solid Psammobia, pi. 

 LXXXIX. fig. 47. 



P. solida. Sowerby, IV. p. 55, pi. 342. 



Transversely elongated, compressed, slightly twisted ; ante- 

 rior side obliquely truncated, with a ridge running from the 

 beaks to the margins, and forming a point ; surface smooth. 



The Upper Marine Formation, Headon Hill. 



5. Psammobia tellinoides. — The Tellina-like Psammo- 

 bia, pi. LXXXIX. fig. 49. 



P. tellinoides. Sowerby, Geo. Tr. 2d Ser. IV. p. 176, pi. 

 21, fig. 6. 



Oblong ovate ; anteriorly slightly rounded, with a few short 

 longitudinal striae ; the rest of the shell smooth ; posterior side 

 rounded ; beaks nearly central. 



The Wealden, Pomiesfield, Sussex. 



6. Psammobia gracilis. — The Slender Psammobia, pi. 

 LXXXIX. fig. 45. 



P. gracilis. Sowerby, Geo. Tr. 2d Ser. IV. p. 341, pi. 16, 

 fig. 12. 



Transversely elongated, the breadth double the length, near- 

 ly cylindrical ; anterior side obliquely truncated, with an acute 

 point below ; surface with many transverse striae, which are 

 elevated at their extremities, and abruptly angular on the 

 truncations. 



The Greensand, Blackdown. 



7. Psammobia Scopula. — The Scopula's Psammobia, pi. 

 LXXXIX. fig. 50. 



P. Scopula. Turton, Brit. Biv. p. 98, pi. 6, fig. 5. 



Transversely oblong ; kidney-shaped ; beaks nearly cen- 

 tral ; sides equally rounded ; anterior side striated in two direc- 

 tions ; the rest of the surface smooth. 



The Coral Crag, Sutton. 



8. Psammobia Florida. — The Florid Psammobia, pi. 

 LXXXIX. fig. 53. 



P.florida. Turton, Brit. Biv. p. 86, pi. 6, fig. 9. 



Transversely oblong oval ; beaks nearly central ; both sides 

 almost equally rounded ; surface with close-set, concentric 

 striEB, and minute longitudinal ones. 



The Coral Crag, Sutton. 



9. Psammobia l^vigata. — The Smooth Psammobia, pi. 

 LXXXIX. fig. 52. 



P. Iceviata. Phillips, Geo. York, I. pi. 4, fig. 5. 



Transversely elongated ; obliquely truncated anteriorly, and 

 rounded pesteriorly ; beaks small, sub-central ; surface smooth. 



The Great Oolite, Cloughton and Scarborough ; and the 

 Inferior Oolite, Blue Wick. 



