CLASSIFICATION. 
9 
Fig. 8. — A Stylommato- 
phorous Pul monate. 
Succinca piitris f'L.), 
Asliley Marsh nr. Bristol, 
Collected by Miss Hele. 
Limnieidw is considered to be identical with the 
branchial chamber of the Pectinibranchs, the 
term Branchiopneusta being used to express 
this difference. Finally the Pnhnonates are 
separated into two Sections 
based npon the position of 
the eyes : the Stylommatopiioha, whicli are 
all terrestrial species and have the eyes placed 
at or near the tips of the u])per tentacles as 
in Helix, Succinea, etc. ; and the Basommato- 
PHORA, which includes those species or genei’a in 
which the eyes ai*e placed at or near the base of 
the tentacles, as in Limnwa. 
Fig. 9. — A Basomma- 
tophorous Pulmonate. 
Limtiaa peregi'a var. 
ovata Drap., 
R. Tome, Doncaster. 
Tlie class Pelecypoda an axe and 7roS-a foot, or axe- 
footed), are exclusively aquatic and pre-eminently marine species. 
Fig. 10. — An Equivalve Inequilateral Pelecypod. 
Unio pictortim (L.), showing left valve, 
Clumber Labe, Notts., collected ))y Mr. C. T. Mu.sson, F.L.S. 
a.s. anal or e.xcurrent siphon ; br.s. branchial or incurrent siphon ; /. foot. 
characterized by the possession of a somewhat linguifoim extensile 
foot, usually more or less adapted for ploughing through or burrowing 
in sand and mud, and are further distinguished by the development 
of an external shell composed of two pieces, or valves, joined to- 
gether by an elastic ligament at the dorsal or upper margin, and 
often furnished in addition with interlocking teeth or denticles at the 
hinge. The term Bivalve, by wbich they are widely and popularly 
known, has reference to this universal presence of two valves to the 
shell, while Lamellibranchiata which is also very generally used 
refers to the lamellar or leaf-like character of their branchiae or 
