Trigonia. 
CONCHIFERA. 
18J 
and a little narrower; beaks obtuse, and nearly central ; basal 
line a little arcuated. 
The Coal Measures, Coalbrook Dale, Staffordshire. 
47. Unio PFIASEOLU8. —The PliasoolaUnio, pi. LXXXVIII. 
fig. 21, 22. 
U. phaseolus. Sowerby, Geo. Tr. 2d Ser. V. pi. 39, fig. 11. 
Considerably elongated transversely ; anterior side very 
short, and pointed; posterior sido lengthened, obtuse, and a 
little flattened; beaks obtuse, and hardly developed; back 
nearly straight ; base a little concave in the middle. 
The Coal Measures, Coalbrook Dale. 
48. Unio robustus.—T he Strong Unio, pi. LXXXVIII. 
fig. 16. 
U. robustus. Sowerby, Geo. Tr. 2d Ser. V. pi. 39, fig. 14. 
Sub-conic, convex ; beaks nearly central and obtuse; both 
sides sloping almost equally from the beaks ; the anterior one 
large and rounded ; posterior sido a little narrowed ; basal line 
convex ; surfaco with strong linos of growth. 
The Coal Measures, Coalbrook Dale. 
49. Unio littoralis.—T he Shore Unio, pi. LXXXVIII. 
fig- 7 . 
U. littoralis. Drapernaud, pi. 10, fig. 20. 
Oblong-ovate ; much inflated ; anterior sido very short, and 
terminating rather abruptly; beaks obtuse ; back considerably 
arcuated ; a little narrowed at the lower posterior end ; basil 
line a little concave; surface with nearly obsolete, shallow 
lines of growth. 
The Coal Measures, Bradford. 
50. Unio dolobratus.—S quared Unio, pi. LXXXVIII. 
fig. 17. 
77. dolobratus. Sowerby, Geo. Tr. 2d Ser. V. pi. 39, fig. 9. 
Sub-quadrate ; rather flat, with an oblique convexity along 
the middle ; anterior side exceedingly short; posterior side 
lengthened ; hinge-line a little curved, base oblique, surface 
rather uneven. 
The Coal Measures, Coalbrook Dale. 
51. Unio aquilinus.—T he Eagle’s-beak Unio, pi. 39, 
LXXXVIII. fig. 23. 
U . aquilinus. Sowerby, Geo. Trans. 2d Ser. V. pi. 39, 
fig. 12. 
Transversely oblong-ovate; beaks very small ; anterior 
side very short with a small terminal projection ; posterior 
side lengthened and pointed ; hinge-line a little curved ; back 
and base slightly convex ; surface with transverse, rather rag¬ 
ged ridges. 
The Coal Measures, Coalbrook Dale, Staffordshire. 
52. Unio parallelus.—T he Parallel Unio,pi. LXXXVIII. 
fig. 25. 
U. parallelus. Sowerby, Geo. Trs. 2d Ser. V. pi. 39, f. 8. 
Transversely elongated, sub-quadrate, and somewhat flat¬ 
tened ; beaks nearly terminal, from whence the side abruptly 
descends in a slightly oblique line; posterior side, back 
and basal lino straight, and parallel to each other; surface 
with well-marked concentric lines of growth. 
The Coal Measures, Coalbrook Dale. 
53. Unio discrepans. — The Discrepant Unio, pi. 
LXXXVIII. fig. 24. 
Transversely oblong-ovate, and much inflated; beaks ob¬ 
tuse ; hinge-line a little curved and oblique ; anterior side 
rounded and of medium length ; a slight hollow below the 
beaks; posterior side elongated ; sub-truucated and contract¬ 
ed at the termination ; back somewhat arcuated ; basal line 
arcuated; a little concave near the posterior side. 
The Coal Measures, Low Moore, near Bradford, Yorkshire. 
54. Unio sub-constrictus. —The Sub-constricted Unio, pi. 
LXXIV. figs. 15, 17. 
U. sub-constrictus . Sowerby, I. p. 83, pi. 33, figs. 2. 3. 
Oblong-ovato, beaks sub-central, incurved and approximate; 
posterior side lengthened ; contracted near the end; anterior 
sido rounded ; hinge-line sub-triangular, a sub-constriction, or 
oblique groove running from the beaks to the margin ; basal 
line arcuated interiorly, and a little concave posteriorly ; sur¬ 
faco smooth, with some shallow concentric furrows. 
In the Argillaceous Ironstone, Derbyshire. 
55. Unio uniformis. —The Uniform Unio, pi. LXI. * * 
fig. 23. 
U. uniformis. Sowerby, I. p. 83, pi. 23, fig 4. Mya ocalis , 
Martin, Pet. Derby, pi. 27, fig. 28. 
Transversely oblong ovate; beaks sub-central; anterior 
side a little rounded, posterior side slightly acuminated ; hinge- 
lino triangular; surface smooth, with a few shallow transverse 
lines of growth. 
In the (flay of the Middle Oolite, Felmersbam, Bedford¬ 
shire, and Derbyshire. 
Genus V.—ALASMODON.— Say. 
Shell thick, generally transversely elongate, but variable in 
form, equivalve, inequilateral; a little gaping posteriorly; 
with or without auricles; umbones for the most part rough 
and decorticated, more so anteriorly; hinge with a lamellar, 
blunted, lateral tooth on the posterior side, situate under the 
ligament, but destitute of one on the anterior side; a short, 
irregularly indented, cardinal tooth in the right valve, which 
locks between the two irregularly crested teeth in the left 
valve ; ligament exterior and much elougated; muscular im¬ 
pressions large, irregular, frequently double, and placed near 
the extremities ; pallial impression deeply defined. 
1. Alasmodon vestustas.— The Ancient Alasmodon, pi. 
LXXII.* fig. 19. 
Pachyodon vestustas. Brown, Ann. Nat. Hist. 1843, pi 
1G,* fig. 7. 
Transversely elongated, compressed; umbones very obtuse 
and depressed ; anterior side short and sub-acute; posterior 
side long, broad, and rounded at the extremity ; hinge and 
basal lines very slightly arcuated ; external surfaco with pretty 
broad, shallow, concentric wrinkles. 
In the Carbonaceous Shale, at Gristhorpe. 
I consider this species as belonging to the genus Alasmodon , with 
which it agrees in all its external characters. 
Tribe II.—TRIGONACEA. 
Primary teeth lamelliform , and transversely striated. 
Genus \ I.—TRIGONIA.— Bruguiere. 
Shell equi valve, inequilateral, transverse, trigonal, some¬ 
times sub-orbicular ; cardinal teeth oblong, laterally compress- 
