LINNEAN SYSTEM.—VERMES. 167 
Triton. Mouth before. Body furnished with arms. Arms 
12, divided, some chelate. 
Sepia. Mouth and body as in Triton. Arms 8-10, beset 
with suckers, 
Clio. Mouth and body as in Triton. Arms 2; membra- 
naceous, dilated like wings. 
Lernza. Mouth and body as in Triton. Arms 2-3; round 
and slender. 
Scyllaa. Mouth and body asin Triton. Arms6; each pair 
at a distance. 
Aphrodita. Mouth before. Body pedunculated, or with 
feet, ovate ; mouth unarmed. 
Nereis. Mouth and body pedunculated, or with feet ; 
elongated ; mouth with claws. 
Medusa. Mouth inferior, central. Body smooth, gelatinous. 
Asteria. Mouth inferior, central. Body coriaceous, prickly. 
Echinus. Mouth inferior, central. Body crustaceous, spined. 
~ 
Ill. Tesracea. 
* Multivalve shells, with many valves. 
Chiton. Shell composed of several transverse plates, ar- 
ranged on the baek. 
Lepas. Valves sessile, of different sizes. 
Pholas. Shell bivalve, with accessory pieces at the posterior 
end. 
** Bivalve shells, of two valves only, furnished with teeth. 
Mya. Hinge with a broad thick tooth, not entering the op- 
posite valve. : 
Solen. Shell open at each end; lateral teeth remote from the 
cardinal teeth. 
Tellina. Hinge with the lateral teeth of one valve not let 
into the other. 
Cardium. Hinge with remote, pointed, lateral teeth. 
Mactra. Cardinal teeth triangular, complicated ; the inter - 
stices hollow. 
Donax. Hinge with a remote lateral tooth, not let into the 
other valve. 
Venus. Hinge with three approximate, divaricating cardinal 
teeth. \ 
Spondylus. Cardinal teeth two, separated by 2 small hollow. 
Chama. Hinge in one valve, with two oblique, obtuse teeth. 
Arca. Hinge with numerous acute teeth. 
Ostrea. Hinge without teeth, but with an ovate hollow. 
Anomia. Teeth none; the rim with a linear depression ; 
valves unequal. 
mM 4 
