196 Mr. Jeffreys on British Mollusca. 



Assiminea Grayana, iii. 70. I have traced this peculiarly local 

 species along the banks of the Thames from Greenwich (its original 

 locality) to about two miles below Gravesend, being a distance of 

 more tban twenty miles. 



A. littorea (Rissoal littorea, iii. 132 and iv. 265), var. pallida. 

 Weymouth. 



Rissoa calathus, iii. 82. In dredged sand from Belfast Bay. 



R. cimicoides (R. sculpt a, iii. 88). Cork Harbour (Mr. Wright). 



R.? fulgida, iii. 128, var. efasciata. South Devon {Mr. Webster). 



R. subumbilicata, Ann. Nat. Hist. 3rd ser. vol. iii. No. 14. p. 108. 

 Southend (J. G. J.) ; Clevedon (Rev. A. M. Norman) ; Birkenhead 

 (Mr. Webster). The last whorl of the shell is never keeled, as in 

 R. ulvce. 



R. Barleei, Jeffr. Ann. Nat. Hist. vol. xix. p. 310 (R. ulvce, var., 

 iii. 143). In deep water, Plymouth (Mr. Webster). A dwarf and 

 thin variety occurs in Arnold's Pond, Guernsey, associated with R. 

 ventrosa, to which latter species (instead of R. ulvce) I would refer 

 the shells mentioned in the 'British Mollusca,' vol. iii. p. 143. I 

 much doubt if R. ulvce is found in Guernsey, as that island is desti- 

 tute of any estuary into which a river flows, which is, I believe, the 

 invariable habitat of that species. 



R. castanea (R. ventrosa, var., iv. 266), Sow. III. Jwrf.pl. 14. f. 1 1. 

 Mr. Pickering found this species about two miles below Gravesend, 

 and not at Grays, as stated in the * British Mollusca.' It is singular 

 that he has not been, any more than myself, successful in redisco- 

 vering the species, although we have both at different times searched 

 the exact spot for it. It can scarcely be questioned that it is speci- 

 fically distinct from R. ventrosa, which is abundant in the same 

 locality. 



R. ventrosa, iii. 138, var. minor. Loughor Marsh, Glamorgan- 

 shire, with R. ulvce. I am not aware of any other instance in which 

 these species have been found associated together. JR. ventrosa 

 usually inhabits brackish water, in ditches and ponds which com- 

 municate with the sea, but receive an accession of salt water only 

 when the tide is at its full, while R. ulvce affects the mud flats of 

 estuaries which are quite covered by the sea at the same period. 

 The habit of the above variety appeared to be different from that of 

 R. ulvce, inasmuch as all the specimens which I noticed of the former 

 were swimming (or rather creeping) underneath the surface of the 

 water, with their shells in an inverted position, while those of R. ulvce 

 were crawling at the bottom, or attached to sea-weeds. Mr. Alder 

 says, with respect to the linguaedental apparatus of these species, 

 " I have examined the tongues of R. ulvce and R. ventrosa, and I 

 find the difference between them so slight as to be scarcely appre- 

 ciable. The principal one is the greater length of the central denticle 

 of the central tooth in R. ulvce. There are also some slight differ- 

 ences in the form of the other teeth ; but the general character is the 

 same." 



Skenea planorbis, iii. 156. A small variety occurs on the shores 

 of Lame Lough, in Ireland, which has a more convex spire ; and it 



