RISSOA. 93 



by a slightly flexuous simple suture : the apical turn is 

 bluntish and very small in proportion ; the rest increase 

 gradually in length, that of the penult not being equal 

 to that of the two preceding volutions collectively. The 

 mouth, whose cavity is vastly diminished in size by the 

 thickness of the surrounding margin, is very obliquely 

 subovate, perfectly smooth internally, and occupies about 

 two-fifths only of the entire length. The outer lip, 

 whose lateral outline is somewhat sinuous, for it advances 

 decidedly towards the base, is very broad, being margi- 

 nated behind by a rather narrow but much projecting 

 rib. This thickened rim, whose edge is curiously marked 

 with a shallow and flattened central excavation, that is 

 barred across with fine raised lines, is continued also along 

 the inner lip, and especially dilated upon the pillar ; the 

 elevated inner margin completes the circuit of the aper- 

 ture. Specimens in general are only the eighth of an inch 

 long, and not quite half so much in breadth. 



This Rissoa is so very easily recognized, that, unlike 

 some of those we have just been describing, its range and 

 localities can be determined with precision. It has a 

 range in depth from low-water-mark to as deep as twenty 

 fathoms. It is frequent in the Channel Islands (S. H.), 

 and along the south coast of England from Sandwich to 

 Cornwall. We have dredged it in twenty fathoms oft' 

 Penzance. It ranges along the east coast of Britain, 

 probably becoming rather scarcer northwards, though fre- 

 quent in shell sand in Northumberland (Alder). It 

 becomes rather scarcer also as we ascend the Irish sea 

 from the Channel, though frequent on the shores of South 

 Wales (Jeft'reys). It has been dredged in from fifteen to 

 twenty fathoms in Caernarvon Bay (M'Andrew) ; and in 

 twelve fathoms in Milford Harbour (M'Andrew and E. F.), 



