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 lohgitudinal 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 Lirmstone. 



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.— .SWer. Min. Conch, t. xxix 



Carboniferous Limestone. 



3. P. ZetJJs.— Smooth, triangular, front rounding beaks incurved. — Sower. 

 Min. Conch, t. xxviii. right hand figure. — Carboniferous Limestone. 



Gen. PRODUCTUS. — Shell bivalve, equilateral, inequi valve; 

 hinge transverse ; one valve convex, the other flat or con- 

 cave. 



1. P. ^owt/ispinws.— 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. — Anomije echinatae, lire Ruth. 314. t. xv. f. 4.— 

 Prod. long. Sower. Min. Conch. Ixviii. f. i. — P. Flemijigii, lb. f. 2.—'Carboni- 

 ferotis Limestone. 



2. P. spinosus Eoundish, verygibbose, obsoletely ribbed ; destitute of the 



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

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



3. P. s/>iwM/osMs..^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. aculeutus. — Roundish, concave valve smooth ; the other with adpres- 

 sed Teflected spines ; gibbous ; front slightly indented ; hinge half the breadth 

 of the shell. — Anomiles acul. M«r/. Derb. t. xxxvii. £ 9, 10 — P. acul. Sower. 

 Min. Conch, t. Ixviii. f. 4. — Carboniferous Limestone. 



5. p. scabriusculus. — Nearly round, flat valve obscurely punctato-striated, 

 the other gibbous, marked with longitudinal strite, 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. 



G. p. scoticus. — Semicircular, with fine longitudinal strioe and a few obso- 

 lete spines, gibbous towards the beak ; sides expanded into the line of the 

 hinge, xvith a mesial depression ; hinge nearly twice tlie length of the shell. 

 — Smier. Min. Conch, t. Ixix. f. 3. and P. antiquatus, lb. t. cccxvii. f. 1,5, 6. 

 — Carboniferous Limestone. 



