578 
MOLLUSCA, SESSILIA. Pentamekus, 
Gen. PENTAMERUS. — Shell bivalve, equilateral, inequi- 
valved ; one valve divided by a longitudinal internal sep- 
tum into two parts, the other by two septa into three parts 
or valves. Beaks incurved, imperforate ; both valves con- 
vex. 
1. P. Circular, with many longitudinal furrows ; tripartite valve 
much depressed, with a short slightly incurved beak; bipartite valve conical, 
gradually produced into a long incurved beak. — Sower. Min. Conch, t. xxviii. 
upper figure. — Carboniferous Limestone. 
2. Y. Aylesfordii — ^Nearly circular, with longitudinal furrows; tripartite 
valve convex, with a prominent incurved beak ; bipartite valve gibbous, in- 
curved, conical, with a much incurved beak — Sower. Min. Conch, t. xxix — 
Carboniferous Limestone. 
3. P. levis — Smooth, triangular, front rounding beaks incurved — Sower. 
Min. Conch, t. xxviii. right hand figure. — Carboniferous Limestone. 
Gen. PRODUCTUS. — Shell bivalve, equilateral, inequivalve; 
hinge transverse ; one valve convex, the other flat or con- 
cave. 
1. P. Eared ; convex valve gibbous, with a mesial depression, 
the other valve, concave ; hinge long ; the convex valve with several unequal 
cylindrical hollow spines ; obsoletely ribbed longitudinally with transverse 
wrinkled layers of growth. — Anomise echinatae, Ure Ruth. 314. t. xv. f. 4.. — 
Prod. long. Sower. Min. Conch. Ixviii. f. i. — P. Flemingii^ Ib. f. 2. — Caid)onu 
ferous Limestone. 
2. P. spmosMs-— -Roundish, very gibbose, obsoletely ribbed ; destitute of the 
mesial depression ; convex valve with many strong spines Sower. Min. 
Conch, t. Ixix. f. 2. — In Carboniferous Limestone. 
3. P. Semicircular, flattish ; hinge long and straight ; convex 
valve gibbous towards the beak, with many small spines spread over it ; the 
other valve also spinous, with irregular depressions, and very concave.— 
Sower. Min. Conch, t. Ixviii. f. 3 — Carboniferous Limestone. 
4. P. aculeatus. — Roundish, concave valve smooth ; the other with adpres- 
sed reflected spines ; gibbous ; front slightly indented ; hinge half the breadth 
of the shell. — Anomites acul. Mart. Derb. t. xxxvii. f. 9, 10 — P. acul. Sower. 
Min. Conch, t. Ixviii. f. ^.-^Carboniferous Limestone. 
5. P. scabriusculus . — Nearly round, flat valve obscurely punctato-striated, 
the other gibbous, marked with longitudinal striae, and prominent tubercles 
ranged nearly in quincunx order; hinge straight, equal to the breadth of the 
shell.— Anomites scab. Mart. Derb. t. xxxvi. f. 5. P. scab. Sower. Min. 
Conch, t. Ixxix. f. 1. — Carboniferous Limestone. 
6. P. scoticus. — Semicircular, with fine longitudinal striae and a few obso- 
lete spines, gibbous towards the beak ; sides expanded into the line of the 
hinge, with a mesial depression ; hinge nearly twice the length of the shell. 
— Sower. Min. Conch, t. Ixix, f. 3. and P. antiquatus, Ib. t. cccxvii. f. 1> 5, 6. 
— Carboniferous Limestone. 
