20 LITTORINID^. 



drew and Forbes discovered it), Skye and Hebrides 

 (Barlee and J. G. J.), Shetland (Forbes and Barlee); and 

 Mr.M'Andrew has dredged it also 15 miles south-west of 

 Mizen Head, co. Cork. Norway (M'Andrew) ; Bohuslan 

 (Loven, as R. sculpta of Philippi) ; off Vigo Bay and 

 Malaga (M'Andrew) ; Gulf of Lyons (Martin, as R. 

 scahra of Philippi) ; 40 miles off Malta in 350 f. (Spratt) . 

 It is a local and somewhat rare species. 



It floats like its congeners, and suspends itself in the 

 water by a single byssal thread. Mediterranean spe- 

 cimens are smaller than ours, and have rather stronger 

 sculpture. Two difterent sizes occur, as is also probably 

 the case with every other species of Rissoa. One of my 

 specimens shows in the middle of the last whorl a dis- 

 tinct varix, caused apparently by a new growth having 

 taken place after the shell had arrived at maturity. 



B. nibbed lengthwise, and spirally striated ; outer lip 

 thickened and reHected. 



10. R. Zetlan'dica^, Montagu. 



Turho Zetlandicus, Mont, in Tr. Linn. Soc. xi. p. 194, t. xiii. f. 3. R. Zet- 

 landica, F. & H. iii. p. 78, pi. Ixxx. f. 1, 2. 



Shell between oval and oblong, tiuTeted or scalariform, 

 solid, nearly opaque, glossy when living or fresh : sculpture, 

 fine and rather sharp longitudinal ribs, of which there are 16 

 on the last whorl, 15 on the penultimate, 14 on the next, and 

 13 on the succeeding whorl, where they usually disappear ; the 

 ribs on the body-whorl do not extend quite to the base, but 

 are cut off by a strong keel or ridge which winds spirally round 

 that part from the upper corner of the mouth ; between this 

 keel and the mouth is a deep groove or depression, which partly 

 arises from the prominence of the keel, and is indistinctly 

 ribbed across ; there is also a slighter and incomplete ridge 

 (sometimes two) near the mouth, between the basal keel and 

 the inner lip ; the labial rib is exceedingly thick and pro- 



* Inhabiting the Shetland seas. 



