The NShell-Collector’s Handbook. 39 
CONSPECTUS OF THE CLASSES, ORDERS, 
FAMILIES AND GENERA OF BRITISH 
LAND AND FRESH-WATER SHELLS. 
(AQUATIC) 
Cuass I.—Matacozoa ELATOBRANCHIA, MENKE. 
Shell a bivalve, the two valves of which are united 
along their dorsal margin by a ligament. Body oval, 
headless; mantle bi-lobed; foot lnguiform, some- 
times provided with a byssus. Respiration accom- 
plished by gills. 
ORDER I.—LAMELLIBRANCHIATA. 
Gills four, leaf-shaped, and arranged in pairs on 
each side of the body. 
Famity I.—Spheriide. 
Shell equivalve, subglobose ; hinge with lateral and 
cardinal teeth. Body with one or two siphons at its 
anterior end. 
1. Spherium, Scop.—Shell nearly equilateral. 
Mantle with two prominent contractile siphons. 
2. Pisidium, C. Pfr.—Shell inequilateral. Animal 
with one siphon. 
4 
Famity Il.—Unionide. 
Shell large, oblong, equivalve, inequilateral. Mantle- 
