5 i MALACOZOA. GASTEROPODA. PECTINIBRANCHIATA. 



1 . Skenea depressa. — Shell orbicular, depressed, trans- 

 parent, horny, with four transversely rugous olivaceous 

 turns. Depressus, pressed down. 



2. Skenea serpidbtdes. — Shell orbicular, depressed, 

 pellucid, glossy, white, flat above, very widely umbi- 



ieate. Named from its resemblance to a Serpula. 



3. Skenea divisa. — Shell orbicular, depressed, pellu- 

 cid, glossy, white, slightly convex and smooth above, 

 spirally striate beneath. Divisus, separated into two parts. 



Genus 4. Littorina. — Shell imperforate, ovoidal, ovato- 

 conical, or subglobose, with the spire short, the last 

 turn very large, ventricose ; the aperture roundish, the 

 peristome incomplete behind, the outer lip bevelled to 

 a thin edge. Named, by Ferussac, from their inhabiting 

 the sea-shore, littiis. Ferussac. 



1. Littorina littorea. — Shell subovato-conical, thick, 

 with the spire half the length of the last turn, which 

 is very convex, longitudinaDy striate ; the aperture 

 roundish, white on the inner lip, streaked on the outer, 

 which forms an acute angle at its junction. Littdreus, 

 residing on the sea-shore. 



2. Littorina rhdis. — Shell subovato-conical, thick, 

 with the spire half the length of the last turn, which 

 is very convex, longitudinally striate, transversely ru- 

 goso-striate ; the aperture oval, the peristome very 

 thick, the outer lip forming an acute angle at its junc- 

 tion. Rudisj coarse. 



3. Littorina saxatilis. — Shell subgloboso-conical, as 

 broad as long, moderately thick, with the spire scarcely 

 a third of the whole length, the last turn somewhat flat- 

 tened above, angulate below, longitudinally striate ; the 

 aperture very large, roundish, the outer lip united at 

 right angles. Saxatilis, living on or among stones. 



4. Littorina tenebrdsa. — Shell subovato-conical, ra- 

 ther thin, with the spire as long as the last turn, which 

 is very convex, longitudinally striulate, transversely ru- 

 goso-striate, the exterior dusky, often banded or tes- 

 selated with lighter tints ; the aperture roundish-oval, 

 the outer lip united at right angles. Te7iebrdsvs, dusky. 



