GINGLYMACONCHA. VENERIDZ. 289 
Lasea rubra occurs on all the western and south-western 
coasts of Devon abundantiy, dwelling in the cracks or inter- 
stices of rocks, or amongst the roots of Fucus digitatus and 
other marine plants. 
My worthy friend, Dr. Goodall, the Provost of Eton, has 
observed it to be not uncommon at Tenby and Weymouth. 
Genus 35. Cycuas. 
Shells ovately globose ; the umbones central and tumid ; the 
hinge with two minute teeth in each valve; the hinder tooth 
in the left valve complicated, those in the right simple; the 
lateral lamellee are transversely elongated, compressed and la- 
melliform. 
The tracheal tubes are unequal, joined ouly at their base ; 
the under one longest with its aperture fringed ; the foot acu- 
minate or lance-shaped, very capable of extension, and at its 
apex as if furnished with a sucker. The mantle is joined to 
the base of the foot even to the tubes. 
1. CycLAS RIVICOLA. 
Shell compressed, concentrically striated with irregular striz ; 
the umbones scarcely prominent. Epidermis pale horn-co- 
loured. Length three-eighths of an inch; height two-eighths 
of an inch. 
Cardium corneum, var., Mont. Test. Brit. 86 ; Lister, Conch. 
fe ehix, £14. 
Cyclas rivicola, Leach, Lam. Hist. Nat. des Anim. sans Vert. 
v. 008. 
This species inhabits muddy rivers; it is common in the 
Thames, the Avon and the Exe. 
2. CYCLAS LACUSTRIS. 
Shells somewhat round, compressed, fragile, with very fine 
concentric strize, the umbones slightly prominent. Epider- 
mis pale fuscous or brown. Length five-tenths ; height three- 
tenths of an inch. 
oO 
