Crassipedes. 
CONCHIFERA. 
227 
almost central; left valve with a strong, central, triangular, 
slightly bifid tooth, which locks into a corresponding pit in the 
opposite valve, on each side of which are triangular transverse 
pits for receiving two small, depressed, cardinal teeth in the 
right valve ; ligament external; two strong muscular impres¬ 
sions in each valve ; pallia! 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 6, fig. 14. 
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 LXL—LUTRARIA.— Lamarck. 
Shell equivalve, inequilateral, thin, transversely ovate or 
oblong; gaping at both sides; the posterior side generally 
the louger, and always gaping more than the other; one valve 
with two thin laminar teeth, one of which is sometimes com¬ 
pound ; the opposito valve 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 carinifera.— The Keeled Lutraria, pi. 
XCII. figs. G, 7. 
L. carinifera . Sowerby, YI. p. 66, pi. 534, 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, 0. 
L . striata. Sowerby, YI. 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 stria?. 
Greensand, Blackdown and Lyme Regis. 
3. Lutraria decurtata. —The Divided Lutraria, pi. 
XCII. fig. 12. 
L. decurtata. Phillips, Geo. York, I. pi. 7, fig. 11. 
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 Cornbrash, Scarborough and Gristborpe; Great Oolite, 
White Nab, Wiltshire ; and the Lias, Rosebury, Yorkshire. 
4. Lutraria primjsva. —The Primoval Lutraria, pi. XCII. 
fig. 15. 
L. primarca. 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 and 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. Lutraria rotund at a. —The Rounded Lutraria, pi. 
XCII. fig. 16. 
L. rotundata. Phillips, Geo. York, I. pi. 12, fig. 6. 
Transversely ovate ; beaks obtuse and incurved ; both sides 
a little narrowod; surface with strong irregular lines of 
growth. 
The Lias, Yorkshire. 
6. Lutraria donaciforme. —The Donax-shaped Lutraria, 
pi. XCII. fig. 17. 
L. donaciforme. 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, Goo. 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, Ill. 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 strim-like 
lines; surface with fine, nearly obsolete, concentric stria?, 
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, Ill. 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 strke-liko wrinkles; pallial im¬ 
pression very large. 
Tho Mammiferous Crag, Brainerton, and the Red Crag, 
Sutton. 
Grand Division IY. — CRASSIPEDES. 
$ 
Mantle entirely or partly united before, foot thick, placed 
posteriorly, shell gaping when closed. 
