Modiola. 
CONCHIFERA. 
171 
rounded and obtuse ; surface smooth; hinge destitute of 
teeth. 
The Lower Greensand, Pulborough and Blackdown. 
5. The Mytilus lanceolatus. — Spear-shaped Mytilus, 
pi. LXXI. fig. 2. 
M. lanceolatus. Sowerby, V. p. 55, pi. 430, fig. 2. 
Lanceolate, a little curved, smooth ; beaks acute ; disk carin- 
ated, smooth ; posterior side flat; anterior side sweeping 
regularly from the beaks to the front; within each beak a 
lamellar tooth. 
Groensand, Parkham and Lyme Regis. 
6. Mytilus subl.evis. —The Ilalf-smooth Mytilus, pi. 
LXXI. fig. 26 *. 
M. sublatvis. Sowerby, Y. p. 56, pi. 430, fig. 3. 
Oblong, triangular, somewhat arcuated; beaks acute ; disk 
obscurely carinated ; front straight; hinge-line parallel, ex¬ 
tending to half the length of the shell, where it is a little 
flattened ; surface with pretty strong lines of growth. 
The Cornbrash, Felmersham, Bedfordshire. 
7. Mytilus pectinatus. —The Toothed Mytilus, pi. LXXI. 
fig. 18. 
M. pectinatus. Sowerby, III. p. 147, pi. 282. 
Rather quadrangular, slightly arcuated ; oblong and gibbosc ; 
beaks produced; front straight; surface with longitudinal, 
rather deep, very regular strkc, which increase in number as 
they diverge towards the front or baso of the valves, from 
which two obtuse angles emanate, giving a quadrangular form 
to the shell. 
The Kitnmeridgo Clay, Weymouth. 
8. Mytilus inzequivalvis.— The Unequal- valved Mytilus, 
pi. LXXI. figs. 6, 7. 
M. incvquiralvis. Sowerby, Geo. Trans. 2d Series, IY. 
p. 342, pi. 17, fig. 16. 
Sub-triangular; beaks nearly central, broad, sub-compressed; 
one valve considerably flatter than the other; surface smooth, 
with faint concentric lines of growth. 
The Greensand, Blackdown. 
0. Mytilus pr^elongus. —The Lengthened Mytilus, pi. 
LXXI. figs. 0, 10. 
M. p radon (/us. Sowerby, Geo. Tr. 2d Ser. IY. p. 342, pi. 
17, fig. 15. 
Considerably elongated, narrow, a little arcuated and carinat¬ 
ed ; hinge-lino nearly straight and rather long, destitute of 
teeth ; surface smooth ; substance of the shell very thick. 
The Greensand, Blackdown. 
10. Mytilus tridens. —The Three-toothed Mytilus, pi. 
LXXI. figs. 7. 8. 
M. tridens. Sowerby, Geo. Tr. 2d Ser. IY. p. 342, pi. 17, 
fig. 14, lb. Min. Conch, p. 55, pi. 439, fig. 1. 
Elongated, convex ; carinated ; beaks acute; hinge-line 
nearly straight ; hinge with three unequal teeth; posterior side 
almost even ; surface very smooth. 
The Greensand, Blackdown. 
11. Mytilus Lyellti. —Lyell's Mytilus, pi. LXXI. f. 27. 
M. Lyellii. Sowerby, Geo. Tr. 2d Ser. IY. p. 346, pi. 21, 
fig. 18. 
Oblong-ovate; a little flattened, especially towards the 
front; much narrowed above and expanded below ; beaks very 
sharp, beneath which the valves are inflated. 
The Weald, Battle and Pounceford. 
12 . Mytilus cuneatus.— The Wedge-shaped Mytilus, pi. 
LXXI. fig. 14. 
M. cuneatus. Phillips, Geo. York, I. pi. 11, fig. 21. 
Somewhat wedge-shaped, short; posterior side nearly 
straight, anterior side much produced; beaks obtuse ; surface 
smooth, with rather wide stria) occupying the lower half of the 
valves. 
The Inferior Oolite, Glaizedale, Yorkshire. 
13. M ytilus cinctus.— The Girdled Mytilus. 
M. cinctus. Portlock, Geo. Rep. p. 426, pi. 25, figs. 5, 6. 
Considerably elongated, narrowed above, with rather acute 
beaks, and expanded and rounded below ; hinge-line a little 
curved; surface smooth, with “fine thread-like striae, proceeding 
from the apex, first straight, and then curving back over the 
back concentrically to the rounded front, proceed straight up 
to the levelled line of the apex, or upper line of the wing.” 
The Silurian Strata, Fermanagh and Lisbellaw Schists, 
Tyrone. 
14. Mytilus semi-rugatus. —The Semi-ragged Mytilus. 
M. semi-rugatus. Portlock, Geo. Rep. p. 430, pi. 25 A, f. 7. 
“ Wide, rudely trigonal; beak sharp, front wide, and usually 
more or less twisted or distorted ; for about one-third of the 
length from the beak transversely wrinkled; longitudinally 
striated or very finely costatod. In r somo specimens the shell 
is much more contorted or arched.” 
Silurian Strata, Fermanagh, Tyrone, Ireland. 
15. Mytilus triangularis. —The Triangular Mytilus. 
M. triangularis. Sowerby, Geo. Tr. 2d Ser. V. pi. 39, 
fig. 16. 
Elongated, sub-triangular, slightly oblique ; sub-com pressed; 
a flat oblique ridge running from the apex to nearly the basal 
margin ; beaks obtuse, surface smooth. 
The Coal Measures, Coalbrook Dale. 
16. Mytilus Danmoniensis. —The Devonshire Mytilus. 
M. Danmoniensis. Phillips, Pal. Fos. p. 37, pi. 17, fig. 61. 
Much elongated and oval; hinge-line short, straight, and 
prominent; base broad and flat. 
Devonian Shales, Newton Bushel. 
17. Mytilus vEquilatfs. —The Equal-sided Mytilus, pi. 
LXXI. fig. 15. 
M. antiquorum. Young shell, Sowerby, III. pi. 275, f. 3. 
Oblong-oval, sub-compressed; sides broad, nearly equal; 
biuge-liue occupying almost half the length of the shell, and 
nearly straight; beaks obtuse, nearly central; surface smooth, 
with remote, slightly-marked lines of growth. 
The Suffolk Crag, Ipswich. 
Genus XXX ^ .—MODIOLA.— Lamarck. 
Shell sub-transverse, equivalve, regular, oblique; form ob¬ 
long, somewhat wedge-shaped, and generally inequilateral; 
anterior side very small and obtuse ; posterior side rounded 
and closed ; anterior margin slightly gaping for the passage of 
the byssus, and forming, with the base, a lino oblique to the 
dorsal one; beaks nearly lateral; outside covered with a 
strong horny epidermis; hinge without teeth ; ligament 
elongated, and sub-external; two muscular impressions, the 
posterior one large, sub-lateral, elongated, and irregular; the 
