Unio. 
CONCHIFERA. 
177 
1. Unio Gerardi. —Gerard's Unio, pi. LXXIII. fig. 23. 
Pachyodon Gerardi. Brown, Ann. Nat. Hist. Dec. 184*3, 
pi. 15. figs. 1, 2. 
Transversely ovate, inflated, thickness equal to half its 
breadth ; umbones produced, rounded, and contiguous; pos¬ 
terior side short and obliquely truncated ; anterior side long 
and sub-truncated ; hingo-line almost parallel ; external sur¬ 
face with a few remote concentric wrinkles or lines of growth. 
I found this species in the Coal Shale at Dalkeith, Mid-Lothian. 
Named in honour of my valued friend, James Gerard, Esq., Retreat, 
East Lothian. 
2. Unio lateralis —The Broad Unio, pi. LXXIII. f. 26. 
Pachyodon lateralis. Brown, Ann. Nat. Hist. Dec. 1843, 
pi. 15, fig. 3. 
Transversely elongated, sub-quadrate, cuneiform ; sides very 
unequal, the anterior one very long, gradually sloping from 
the umbones, and terminating in an obliquely truncated point; 
posterior ono very short; umbones produced, with acute but 
not inflected beaks. Length somewhat more than half an 
inch ; breadth nearly an inch and a-half. 
In the Coal Shale, Whitehaven. 
3. Unio sulcatus. —The Furrowed Unio, pi. LXXIII. 
figs. 28, 29. 
Pachyodon sulcatus. Brown, Ann. Nat. Hist. Dec. 1843, 
pi. 15, figs. 4, 5. 
Sub-triangular, rather compressed ; umbones prominent, very 
close, slightly reflected, sub-acute, and placed considerably to 
ono side; general surface smooth, with inequidistant concen¬ 
tric furrows ; posterior side arcuated, with a rounded point situ¬ 
ate low ; anterior side gently rounded ; basal line nearly paral¬ 
lel. Length one and a-half inch ; thickness one half inch. 
The Shale near Whitehaven. 
This species is liable to some variety in external contour. 
4. Unio rugosus. —The Rugged Unio, pi. LXXIII. figs. 
14, 15. 
Pachyodon rugosus. Brown, Ann. Nat. Hist. Dec. 1843, 
pi. 15, figs. 6, 7. 
Sub-triangular, greatly ventricosc in proportion to its size, 
its depth beiug equal to five-sixths of its wholo length ; um¬ 
bones very prominent, situate considerably to one side, point¬ 
ing posteriorly, and remote from each other; anterior side ab¬ 
ruptly descending and rounded ; posterior side gradually slop¬ 
ing and considerably more acute than the other; ligament 
produced ; external surface with unequal, rugose, concentric 
wrinkles. Length two inches five-eighths ; breadth three 
inches and a-half; thickness two inches and a quarter. 
The young shells are much more rugosely wrinkled than the 
adult. 
Found in the Ironstone Shale at Sheden, by Mr S. Gibson of 
Ilebden Bridge, and in his cabinet. 
5. Unio sub-rotundus. —The Sub-rotund Unio, pi. 
LXXIII. fig. 22. 
Pachyodon sub-rotundus. Brown, Ann. Nat. Hist. Dec. 
1843, pi. 15, fig. 8. 
Sub-rotund; umbones sub-central, produced, blunt, and 
somewhat remote from each other ; hinge-lino considerably 
arcuated ; surface with irregular, acute, concentric wrinkles ; 
thickness about equal to half its length. 
The Coal Shale, Oldham. 
6. Unio ripennis. —Two-winged Unio, pi. LXXIII. f. 27. 
Pachyodon bipennis. Brown, Ann. Nat. Hist. Dec. 1843, 
pi. 15, fig. 9. 
Transversely elongated, somewhat hatchet-shaped; sides 
unequal; umbones produced and remote; hinge and basal 
lines nearly parallel; anterior side short and rounded ; poste¬ 
rior side elongate, and obliquely sub-truncate from the hinge¬ 
line, terminating below in a short, slightly acuminated curve: 
surface rather smooth, with a few distant, transverse, shallow 
grooves. 
The Ironstone Shale at Low Moore, Yorkshire. 
7. Unio Dawsoni. —Dawson's Unio, pi. LXXIII. fig. 3. 
Pachyodon Dawsoni. Brown, Ann. Nat. Hist. Dec. 1843, 
pi. 15, fig. 10. 
Orbicular; umbones central, large, produced and remote; 
surface nearly smooth, with only a few nearly obsolete concen¬ 
tric wrinkles ; thickness equal to more than half its diameter. 
Found in the Ironstone Shale at Low Moore, near Bradford, 
aud is in the Cabinet of Mr S. Gibson, and named in honour 
of Miss Dawson of Low Moore, an accomplished geologist. 
8. Unio nanus. —Tho Little-vessel Unio, pi. LXXIII. f. 7- 
Pachyodon nanus. Brown, Ann. Nat. Hist. Dec. 1843, pi. 
16, fig. 1. 
Smooth, posterior side elongated, and obliquely sub-truncate 
above; sub-acute above ; anterior side rounded ; umbones pro¬ 
duced and rounded ; hinge-line arcuated. 
Coal Shale at Middleton, near Leeds. 
9. Unio Rhindii. —Rhind’s Unio, pi. LXXIII. fig. 5. 
Pachyodon Rhindii. Brown, Ann. Nat. Ilist. Dec. 1843, 
pi. 1G, fig. 2. 
Sub-acute at both extremities ; basal lino considerably arcu ¬ 
ated, rather produced opposito the umbones ; posterior side 
turned slightly upwards; umbones sub-central, rather pro¬ 
duced, and very close; hinge-line curved ; surface with trans¬ 
verse, shallow, irregular wrinkles. Length equal to two-thirds 
of its breadth. 
In tho Coal Shale, Polmont, Stirlingshire, by my friend 
William Rhind, Esq., author of “ The Ago of the Earth,” &c. 
10. Unio amygdala. —The Almond Unio, pi. LXXIII. 
fig. 4. 
Pachyodon amygdala. Brown, Ann. Nat. Hist. Dec. 1843, 
pi. 1G, fig. 3. 
Inflated, anterior side rounded ; posterior side acuminated, 
with an acute beak-like termination ; umbones rather obtuse 
and remote; basal line considerably arcuated ; surface with 
many irregular acute wrinkles. 
Ironstone Shale, Low Moore, Yorkshire. 
11. Unio exoletus. —The Worn Unio, pi. LXXIII. f. 25. 
Pachyodon exoletus. Brown, Ann. Nat. Hist. Dec. 1843, 
pi. 16, fig. 4. 
Shell transversely elongate, its breadth about double its 
length ; surface quite smooth ; umbones blunt, placed near to 
the anterior side, which is round ; posterior side acuminated 
and sub-acute; hinge-line slightly arcuated ; basal lino nearly 
parallel; thickness somewhat more than half its length. 
Ironstone Shale, Low Moore, near Bradford. 
12. Unio dubius. —Tho Doubtful Unio, pi LXXIII. f. 13. 
Pachyodon dubius. Brown, Ann. Nat. Ilist. Dec. 1843, 
pi. 1G, %. 5. 
Sub-ovate, both sides rounded ; umbones slightly produced 
2 R 
