228 
COiNCIdlFERA. 
Mya. 
Tribe I.—MY ARIA. 
Ligament internal ; a broad, spoon-shaped tooth in eacli 
valve, or in one only ; shell gaping at both sides, or at one 
only. 
Genus LXII.—MYA.— Linnaeus . 
Shell trausversc, nearly cquivalve, gaping at both extremi¬ 
ties, but widest at the posterior end; one valve with a large 
compressed, dilated, spoon-shaped, vertically projecting tooth ; 
the opposite valve destitute of teeth ; two lateral, distant, 
muscular impressions, the anterior one narrow, and the poste¬ 
rior one orbicular; mantle muscular impression with a large 
sinus; ligament internal, large, and fixed in the cavity of the 
tooth, in one valve, and to a large sub-umbonal cicatrice in 
the other. 
1. Mva rotund at a .—The Rounded Mya, pi. XCII. f. 22. 
M. rotundata. Sowerby, Silur. Syst. pt. II. p. G13, pi. G, 
%. 1 . 
Shell transversely oblong, convex ; beaks obtuse, and situate 
near the anterior side, which is separated by a concave space 
from the middle of the valves; posterior side rounded ; surface 
wrinkled transversely. 
Tliis species strongly resembles Cypricardia undata, but will at once 
be distinguished by its want of a lunette. 
From the Ayraestry Limestouo, or Middle Ludlow Rocks, 
at Caynham Camp, near Ludlow. 
2. Mya mandibula. —The Jaw Mya, pi. XCII. fig. 13. 
M. mandibula . Sowerby, I. p. 93, pi. 43. 
I r msversely elongated, its breadth being once and a half its 
length; gibbose; disk flattened in the middle; anterior sido 
square, gaping, the opening oblong; posterior side somewhat 
straight; depth about two thirds its length ; surface with about 
25 transverse undulations; beaks pointed and incurved. 
Uppm* Greensand, Devizes and Blackdown; the Gault, 
Isle of AN ight and Dorsetshire; and the Lower Greensand, 
Pulborough and Lyme. 
3. Mya augustata.—T he Xarrowcd Mya, pi. XCII. figs. 
2G, 27, 28, 2.9. 
J/. augustata. Sowerby, VI. p. 57, pi. 531, fig. 1. 
Transversely elongated; its width sometimes thrice its 
length ; valves unequal ; shell thin and antiquated; irregularly 
compressed ; both sides obtuse and gaping; base of the lesser or 
right valve concave; beaks small, placed nearest the anterior 
side. Hinge like those of M. sub-angulata and plana. 
Tho Upper Marl, Colwell Bay. 
4. Mya ovalis.—T he Oval Mya, pi. XCII. figs. 24, 25. 
M. oval is. Turton’s Brit. Bia. pi. 3, fig. 1, 2. Mya pullus . 
Sowerby, VI. p. 58, pi. 531, fig. 2. 
Transversely ovate; its length a littlo more than half its 
width ; anterior side longest and rounded; posterior sido 
somewhat pointed ; surface concentrically striated, and a littlo 
compressed ; lines of growth well defined. 
Mamniiferous Crag, Postwick ; the Red Crag, Butloy, and 
and the Pleistocene Marino Series, Isle of Bute. 
5. Mya arenaria. —The Sand Mya, pi. XCII. fig. 23. 
M. arenaria. Sowerby IA r . p. 88, pi. 3G4. 
Transversely ovate ; anterior side pointed ; posterior side 
rounded ; surface with concentrical sub-strim and undulations. 
The Pleistocene Marine Formation, Ayr and Dalmuir, Dum¬ 
bartonshire ; tho Mamniiferous Crag, Bramerton, and Red 
Crag, Sutton. 
G. Mya lata.—T ho Broad Mya, pi. XCIII. fig. 4. 
M. lata . Sowerby, I. p. 185, pi. 81. 
Ovate; length about two thirds its width, compressed ; an¬ 
terior side acuminated and truncated, having an arcuated 
margin, slightly gaping; beaks rather produced and acute ; 
surface smooth, with a few shallow uudulations ; tooth very 
large. 
The Mamniiferous Crag, Bramerton, and tho Red Crag, 
Sutton. 
7. Mya jequata. —The Equal Mya, pi. XCII. fig. 20. 
JI. cvquata . Phillips, Geo. York, I. pi. 11, fig. 12. 
Transversely oblong ovate; beaks nearly central, and obtuse; 
sides equally rounded ; surface smooth. 
The Inferior Oolite, Blue AVick, Coldmoor. 
8. Mya calciformis. —The Shoe-Shaped Mya,pi. XCIII. 
fig. G. 
M . calciformis. Phillips, Geo. York, I. pi. 11, fig. 3. 
Transversely lengthened, short, rounded at both extremities; 
the posterior side a little narrowed ; a slight inflection towards 
tho centre at the base; surface smooth. 
Tho Ivelloways Rock, Scarborough, and tho Inferior Oolite, 
Blue Wick, Cheltenham. 
9. Mya dilata. —The Dilated Mya, pi. XCII. fig. 18. 
M. dilata . Phillips, Geo. York, I. pi. 11, fig. 4. 
Much elongated transversely, a little twisted; anterior side 
a little narrow at tho extremity; posterior side considerably 
dilated and truncated, acute above and below ; beaks sub-cen¬ 
tral, curved backwards, between which and the angle the back 
is concave ; basal line nearly straight. 
The Inferior Oolite, Glaizedale. 
10. Mya l.eviuscula.—S mooth Mya, pi. XCII. fig. li. 
M. Iccviuscula. Sowerby, Geo. Tr. 2d Ser. IV. p. 340, 
ph 1G, fig. G. 
Transversely oblong, somewhat square; a depression from 
tho beaks to the base in the centre of tho valves; beaks rather 
prominent; sides bluntly rounded ; surface smooth, with a few 
transverse wrinkles. 
Tho Greensand, Blackdown. 
11. Mya phasiolina.—T he Little Pheasant Mva, pi 
XCII. fig. 21. 
M. phasiolina . Phillips, Geo. York, I. pi. 2, fig. 13. 
An elongated ellipsis, both sides equally rounded ; beaks 
obtuse; surface smooth. 
The Speeton Clay, Speeten, Yorkshire. 
12. Mya troncata.—T he Truncated Mya, pi. XCIII. f. 1. 
M. truncata. Brown, Illust. Rec. Conch. Brit., p. Ill, pi. 
45, fig. 2. 
Sub-ovate ; anterior sido rounded ; posterior side much trun¬ 
cated, and gaping widely ; hinge lino nearly straight; basal 
line almost parallel to the back, and slightly hollow in the 
middle ; surface with numerous concentric wrinkles. 
Pleistocene Marine Formation, Ayrshire, the Red Crag, 
Sutton, and the Coral Crag, Ramshot. 
