Mr. Jeffreys on British Mollusca. 195 



been detected in the adjacent sea. In texture and appearance, all 

 these fossils are very different from the shells taken on the Turbot 

 Bank. Local information has satisfied me that none of the last- 

 mentioned shells could have been brought from any distance by 

 marine currents ; and indeed I have found nearly all the species 

 living in the immediate locality. 



M. ? costulata (Skeneal costulata, Hi. 167). Mr. Waller found 

 two specimens with the last, and in the same condition, one of which 

 he has obligingly presented to me. Mr. Barlee has also taken a 

 small specimen in dredged sand from the Shetlands. 



Adeorbis subcarinatus, ii. 541. The supposed operculum of this 

 unknown mollusk (p. 543) is the Spirillina perforata of Williamson 

 (Mon. Brit. Rec. For. in the publications of the Ray Society, p. 92. 

 f. 202), and belongs to the Foraminifera. 



Bithynia Leachii, hi. 1 6. Neighbourhood of Boston {Mr. Barlee); 

 var. minor, Northamptonshire (J. G. J.). 



Littorina littorea, iii. 29. On the shore of the Thames, at South- 

 end, nearly all the specimens are more or less eroded, and so much 

 so in some cases as to appear distorted. This cannot, I think, be 

 owing (as supposed by some naturalists) to the admixture of fresh 

 water with the sea, because in the same locality, where a small 

 stream empties itself into the Thames, none of the specimens are 

 similarly affected, while on the sea-shore at Tenby, where there is 

 no flow or infiltration of fresh water, dwarf specimens of Mytilus 

 edulis (var. incurvatus) are partially eroded, and the limestone rocks 

 are fretting away from apparently the same cause. On the opposite 

 coast of North Devon the Bur pur a lapillus presents a similar case of 

 erosion ; and the Chthamalus punctatus derives its specific name 

 from such marks. Other instances of the same kind will doubtless 

 occur to many of my readers. I believe this erosion is caused by 

 the action of carbonic acid, which is evolved by sea-water in con- 

 siderable quantities under certain conditions, aided by tbe gyratory 

 motion and reflux of the tide. 



L. fabalis, iii. 49. This variety of L. litt oralis, is found with the 

 voung and an intermediate form of the typical species on the shores 

 of Larne Lough, in the north-east of Ireland ; and it confirms my 

 former impression that these two so-called species ought to be united. 

 A similar intermediate gradation of form occurs in the same place 

 with respect to L. rudis and its variety L. tenebrosus. 



Lacuna iabiosa, Lov. iii. 66. In dredged sand from Belfast Bay ; 

 a single specimen. 



L. crassior, iii. 67. Specimens from Guernsey and Belfast Bay 

 have a distinct canal or groove in the columella, evidently showing 

 its generic position, I am now enabled to add a note of the animal, 

 which settles the question. It is of a yellowish-white colour, having 

 two subulate and slender tentacles, with the eyes placed on short 

 peduncles at their external base ; proboscis long and narrow ; two 

 rather long caudal filaments, one on each side of the operculigerous 

 lobe. The creature is active in its habits, and seems fond of crawl- 

 ing out of water. 



13* 



