378 MOLLUSCA. SESSILIA. Pentamerus. 



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. Knightii. — 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. — Sovjer. Min. Conch, t. xxviii. 

 upper figure. — Carboniferous Limestone. 



2. P. 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. longispintis.— 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, lire Ruth. 314. t. xv. f. 4. — 

 Prod. long. Sower. Min. Conch, lxviii. f. i. — P. Flemingii, lb. f. 2. — Carboni- 

 ferous Limestone. 



2. P. spinosus Roundish, very gibbose, obsoletely ribbed ; destitute of the 



mesial depression ; convex valve with many strong spines — Sower. Min. 

 Conch, t. lxix. f. 2.— In Carboniferous Limestone. 



3. P. spinulosus 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. lxviii. 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. lxviii. f. 4. — Carboniferous Limestone. 



5. P. scabrhisculus. — Nearly round, flat valve obscurely puncta to-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. lxxix. 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. lxix. f. 3. and P. antiquatus, lb. t. cccxvii. f. 1, 5, 6. 



— Carboniferous Limestone. 



