GASTEROPODA. PLEUROBRANCHID&. 29 
This species is by no means uncommon at the mouth of the 
Yalm river; at Salcombe ; in the Kingsbridge Estuary, near 
the Saltstone ; and in Millbay, near Plymouth. 
I have named this species after Montagu, by whom it was 
first discovered ; and have rejected the term Plumula, since it 
is equally applicable to all the species of Pleurobranchide. 
Genus 11. Oscanivs. 
Os reconditum, lamella crassiuscula, anticé utrinque cornuta, 
superné instructum. Pallium pede multo angustius, anticé et 
postict emarginatum. Branchie valdé elongate. Pes posticé 
rotundatus, integer. Testa subcalcarea, tenuissima, ad basin 
sinistrorsum subreflexa. 
Mouth concealed, furnished below with a thickish lamella, 
which has a horn-like appendage on each side, anteriorly. 
Mantle much narrower than the foot, notched anteriorly and 
posteriorly. Branchiz very much elongated. Foot entire, 
rounded behind. 
Shell somewhat calcareous, very slender, the left side at its 
base slightly reflexed. 
1. OscaNIUS ARGENTATUS. 
O. testa argenteo-nitente subcarnea, concentrice crenata. 
Bulla membranacea, Mont. Trans. Linn. Soc. xii. 185. t. 12. 
fig. 4; Turt. Conch. Dict. 25. 
Lamellaria membranacea, Mont. loc. cit. fig. 3, pessima. 
Animal pallio superné verrucoso, verrucis nonnullis longioribus 
conicis. 
Habitat in estuario prope Salcombe in Danmonid Australi, 
rarior. 
Shell pale flesh-red with a silvery lustre, concentrically 
wrinkled. 
Mantle varied with brownish streaks, its dorsal aspect verru- 
cated ; some of the protuberances larger than the rest, and 
conic. Lower aspect of the foot pale luteous, more or less 
spotted with grey. 
Length of the animal two inches; of the shell an inch and 
quarter. 
