Grassipedes. 



CONCHIFERA. 



227 



almost central ; left valve with a strong, central, triangular, 

 slightly bifid tooth, which locks into a corresponding pit in the 

 opposite valvo, on each side of which are trianguhir transverse 

 pits for receiving two small, depressed, cardinal teeth in the 

 right valve ; ligament external ; two strong muscular impres- 

 sions in each valve ; pallial impressions entire. 



1. Mactra triangularis. — The Triangular Mactrina. 



M. triangularis. Brown, Illus. Rec. Conch. Brit. p. 108, 

 pi. 40, fig. 25. Goodallia triangularis. Turton, Brit. Biv. 

 p. 77, pi. e, fig. U. 



Sub-triangular, rather strong ; sides slightly unequal ; sur- 

 face smooth ; internal margin strongly crenated ; diameter 

 about a quarter of an inch. 



The Pleistocene Marine Formation, Ireland. 



Genus LXI.—LUTRARIA.—Zawarc/t. 



Shell equivalve, inequilateral, thin, transversely ovate or 

 oblong; gaping at both sides; the posterior side generally 

 the longer, and always gaping more than the other; one valve 

 with two thin laminar teeth, one of which is sometimes com- 

 pound ; the opposite valvo with three teeth, the central one 

 compound in some instances, and the posterior one slender and 

 compressed ; two distant lateral muscular impressions ; mus- 

 cular impression of the mantle with a large sinus ; ligament 

 internal, situate in a deltoidal, oblique, internally projecting, 

 spoon-shaped pit, with a prominent margin placed next to the 

 teeth in each valve. 



1. Lutraria cahinifera. — The Keeled Lutraria, pi. 

 XCII. figs. 6, 7. 



L. carinifera. Sowerby, VI. p. 66, pi. SSI, fig. 2. 



Transversely oval ; its width about twice its length ; con- 

 vex ; surface longitudinally striated ; posterior side truncated, 

 smooth, bounded by an obtuse keel, and with its edge 

 straight. 



The Lower Chalk, Dowlands, Devonshire. 



2. Lutraria striata. — The Striated Lutraria, pi. XCII. 

 figs. 8, 9. 



L. striata. Sowerby, VI. p. 65, pi. 534^ fig. 1. 



Transversely oval, its length being two-thirds its width ; 

 compressed ; posterior side smallest, rather pointed, gaping 

 and turned outwards ; beaks prominent ; surface with nume- 

 rous equidistant concentric striae. 



Greensand, Blackdown and Lyme Regis. 



3. Lutraria decurtata. — The Divided Lutraria, pi. 

 XCII. fig. 12. 



L. deciirtata. Phillips, Geo. York, I. pi. 7, fig. H. 



Transversely oblong, elongated ; beaks obtuse and incurved; 

 placed towards the anterior side ; both sides rounded, surface 

 with several strong transverse furrows below the beaks ; disk 

 divided by a strong line of growth ; remaining portion 

 smooth. 



The Combra-sh, Scarborough and Gristhorpe ; Great Oolite, 

 White Nab, Wiltshire ; and the Lias, Rosebury, Yorkshire. 



4. Lutraria pri.m.s;va. — The Primeval Lutraria, pi. XCII. 

 fig. 15. 



L. prim<Bva. Portlock, Geo. Sur. p. 441, pi. 36. fig. 5. 



Transversely elongated, somewhat square, and a little 

 twisted ; beaks tumid, situate near the posterior side, which 

 is flattened above an<l a little curved below ; anterior side a 

 little rounded ; back and basal lines nearly parallel ; surface 

 with irregular concentric stria), and some indistinct lines of 

 growth. 



The Carboniferous Limestone, Carnteel, Tyrone. 



5. LuTiiARiA rotundata. — The Rounded Lutraria, pi. 

 XCII. fig. ] 6. 



L. rotumhita. Phillips, Geo. York, I. pi. 12, fig. 6. 



Transversely ovate ; beaks obtuse and incurved ; both sides 

 a little narrowed; surface with strong irregular lines of 

 growth. 



The Lias, Yorkshire. 



6. Lutraria donaciforme. — The Donax-shaped Lutraria, 

 pi. XCIL fig. 17. 



L. donaei/orme. Phillips, Geo. York, I. pi. 12, fig. 5. 



Transversely oblong ovate ; rather convex ; a ridge, extend- 

 ing from the obtuse beaks, terminates on the base ; surface 

 smooth, with strong lines of growth ; basal lines nearly straight, 

 with a slight hollow. 



The Lias, Rosebury, Yorkshire. 



7. Lutraria gibbosa. — The Gibbous Lutraria, pi. XCII. 

 fig. 10. 



L. gibbosa. Phillips, Geo. York, I. pi. 9, fig. 6. 



Transversely elongated, gibbous ; both sides rounded ; the 

 posterior one a little produced below ; beaks depressed, sur- 

 face smooth, with strong, regular, concentric lines of growth ■ 

 on the posterior side a few remote radiations extending from 

 the beaks. 



The Great Oolite, Cloughton. 



8. Lutraria elliptica. — The Elliptical Lutraria, pi. 

 XCII. fig. 14. 



L. elliptica. Brown, 111. Rec. Conch. Brit. p. 109, pi. 43, 

 figs. 2, 3. 



Transversely oblong ovate, compressed ; longer side with a 

 shallow groove, emanating from the beak and extending to the 

 basal line, over which there are some irregular stria;-like 

 lines ; surface with fine, nearly obsolete, concentric strife, 

 and a few wrinkles. 



The Red Crag, Sutton ; Coral Crag, Ramshot ; and the 

 Great Oolite, Cloughton. 



9. Lutraria compressa. — The compressed Lutraria, pi. 

 XCII. fig. 19. 



L. compressa. Brown, 111. Rec. Conch, Brit. p. 109, pi, 

 43, fig. 4. 



Transversely sub-ovate ; beaks rather obtuse ; anterior side 

 rounded ; the other slightly acuminated ; surface covered 

 with pretty strong transverse strine-like wrinkles; pallial im- 

 pression very largo. 



The Mammiferous Crag, Bramerton, and the Red Crag, 

 Sutton. 



Grand Division IV.—CRASSIPEDES. 



Mantle entirely or partly united before, foot thick, placed 

 posteriorly, shell gaping when closed. 



