Unio. 
CONCIIIFERA. 
179 
Pachyodon transversus. Brown, Ann. Nat. Ilist. Dec. 
1843, pi. 16,* fig. 5. 
Transverse!v elongated; umbones blunt and obliquely 
rounded ; anterior side short, rounded, and slightly produced at 
the extremity; posterior side long, gradually declining from 
the umbones, ending in an obliquely truncate termination, 
rather acutely beaked below ; hinge-line nearly straight, basal 
liue with a slight flexure posteriorly ; surface rather smooth. 
Coal Shale at Middleton, near Leeds. 
24. Unio mi mat us. —The Buried Unio, pi. LXXII. f. 18. 
Pachyodon humatus. Brown, Ann. Nat. Hist. Doc. 1843, 
pi. 16,* fig. 6. 
Oblong-ovate, considerably inflated; umbones large, pro¬ 
duced, and slightly inflected; anterior side rounded, posterior 
side sub-acute ; hinge-line nearly parallel; basal margin a little 
arcuated ; surfaco with strong concentric wrinkles. 
In the Coal Shale at Gristhorpe Bay. 
25. Unio leveDensis. —The Coarse Unio, pi. LXXIII.f.30. 
Pachyodon levedensis. Brown, Ann. Nat. Hist. Dec. 1843, 
pi. 16,* fig. 8. 
Sub-triangular, wedge-shaped; umbones rounded, situate 
considerably to one side ; anterior side very short and abruptly 
descending; posterior side long, acuminated, its superior 
margin gradually inclining to a truncated termination ; basal 
margin nearly straight; surface with transverse antiquated 
wrinkles. 
Coal Shale at Middleton. 
26. Unio pyramidalus.— The Pyramidal Unio, pi. 
LXXI1I. f. 19. 
Pachyodon pyramidalus. Brown, Ann. Nat. Hist. Dec. 
1843, pi. 16,* fig. 9. 
Sub-triangular, cuneiform, somewhat pyramidal; umbones 
larjre, contiguous, extremely obtuse; anterior side very short, 
abruptly descending and rounded below ; posterior side elon¬ 
gated, its superior line gradually descending to a blent acumi¬ 
nated termination, thick or. the anterior side, and becoming 
rapidly compressed posteriorly ; base acute, slightly flexuose 
and fhin at the edge ; surfaco with shallow irregular wrinkles; 
thickness equal to two-thirds its length. 
Ironstone Shale at Low Moore ; also in Shale at Woodhall, 
near Edinburgh. 
27. Unio Aldamii. —Aidant's Unio, pi. LXXII1. fig. 18. 
Pachyodon Aldamii. Brown, Ann. Nat. Hist. Dec. 1843, 
pi. 16,* fig. 3. 
Sub-compressed, flexuose, and sub-triangular ; umbones sub¬ 
central, very obtuse, set one-eighth of an inch apart; hinge¬ 
line slightly arcuated ; anterior side abruptly descending from 
the umbones, beneath which it is slightly rounded, with a 
flexure below, somewhat produced on the margin immediately 
under the umbones ; posterior side gently sloping and rounded, 
with a shallow furrow emanating from below the umbones, 
and rapidly widening, terminates on the base; basal lino 
flexuose. Length one inch five-eighths ; breadth two inches 
one-eighth ; thickness one inch. 
The greatest thickness of the shell is at the middle of the 
disk, from whence it rapidly becomes thin towards the 
margins. 
Coal Shale at Whitehaven. 
Named in honour of Miss Aldam of Leeds, an excellent concliologist. 
28 . Unio cordiformis. —The Heart-shaped Unio, pi. 
LXIV. fig. 21. 
U. cordiformis . Sowerby, VI. p. 191, pi. 59.5, fig. 1. 
Hcart-shapod ; posterior sido rounded ; anterior side pointed, 
its length and thickness being nearly equal; beaks rounded, 
large, and considerably produced. 
The Weald Clay, Tilgate Forest. 
29. Unio sub-truncatus. —The Sub-truncated Unio, pi. 
LXXIV. fig. 6. 
U. suh-truncatus. Sowerby, Geo. Trans. 2d Ser. IV. p. 
346, pi. 21, fig. 1.5. 
Ovate, compressed; edges of the valves obtuse; posterior 
sido obliquely wedge-shaped ; beaks small and a little remote. 
The Hastings Sand, Sussex. 
30. Unio Martini. —Martin's Unio, pi. LXXIV. fig. 7. 
U. Martini. Sowerby, Geo. Tr. 2d. Ser. IV. p. 346, pi. 
21, fig. 7. 
Convex, beaks slightly produced and nearly central; poste¬ 
rior side very large and rounded; anterior sido somewhat 
acute ; surface nearly smooth. 
The Weald Clay, Ilenhurst, Sussex. 
31. Unio Mantellii. —Mantell’s Unio, pi. LXXIV. 
fig. 16. 
U. Mantellii. Sowerby, Geo. Tr. 2d Ser. IV. p. 346, pi. 
21, fig. 14. 
Oblong-ovate, compressed, with tho dorsal and basal margins 
nearly parallel and straight; posterior side short; anterior 
side lengthened ; beaks slightly produced; surface smooth ; 
length about equal to half the breadth. 
The Weald Clay and Hastings Sand, Sussex. 
32. Unio tumidus. —The Swollen Unio, pi. LXXIV.* 
figs. 5, 6. 
U. tumidus . Brown, Illust. Land and Fresh-water Shells, 
p. 110, pi. 21, figs. 8, 9. 
Somewhat cylindrical, or wedge-shaped; much inflated, 
with tho beaks produced; anterior side short, rounded ; poste¬ 
rior sido long, gradually sloping from the beaks; the termina¬ 
tion sub-truncated ; cardinal tooth large, thick, and elevated, 
with tho edge finely serrated, and double in the opposite valve ; 
muscular impressions small; surfaco with strong concentric, 
wrinkles. 
Tho Pleistocene Fresh-water Formation, Sutton, Grays, and 
Cropthorn. 
33. Unio ovalis. —The Oval Unio, pi. LXXIV.* f. 3, 4. 
U. ovalis. Brown, Land and Fresh-wator Shells, p. Ill, 
pi. 18, figs. 4, 5. 
Transversely ovate ; hinge-line arcuated ; beaks prominent, 
wrinkled, and closely approximate; right valve with a strong 
double, erect, cardinal tooth, the higher portion situate below 
the beak, and considerably elevated above tho margin, with 
two long, oblique, lateral teeth; muscular impressions of mo¬ 
derate size, the anterior ones deep ; left valve with a simple, 
erect, oblique, cardinal tooth, and a long, elevated, lateral one 
which fits into the cleft between those of the opposite valve. 
Tho Pleistocene Formation, Cropthorn. 
34. Unio Solandri. —Solander’s Unio, ph LXXIV. f. 10. 
U. Solandri. Sowerby, Min. Conch. VI. p. 29, pi. 517, 
Fleming, Brit. An. p. 417. 
Shell transversely oblong-ovate, compressed, thin; hinge- 
