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 serpuloides. Shell orbicular, depressed, 

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



icate. 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 imperf orate, 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 Femssac, from their inhabiting 

 the sea-shore, littus. Ferussac. 



1. Littorina lift area. Shell subovato-conical, thick, 

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

 is very convex, longitudinally striate ; the aperture 

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

 which forms an acute angle at its junction. Litt6reus, 

 residing on the sea-shore. 



2. Littorina rudis. 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. Rudis, 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. Saxdtilis, 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. Tenebrdsus, dusky. 



