GASTEROPODA. 



LACUNA (MEDORIA) TEREBELLATA, Nyst. 



MELANIA TEREBELLATA, Nyst. Coq. foss. de Beige, p. 413, pi. xxxviii, fig. 12, 1843. 

 PALUDESTKINA S. Wood. Crag Moll., vol. i, p. 109, tab. xii, fig. 7, 1848. 



EULIMENE 1st Supplement, p. 65, 1872. 



This shell was figured by myself in the ' Crag Moll.' under the generic name of 

 Paludestrina. In my first Supplement I, in my perplexity, grouped it in a new genus, 

 in which I proposed to embrace another crag shell, viz., Eulimene. It is not, I think, 

 either a freshwater or an estuarine shell, neither does it belong either to Paludina or to 

 Littorina. 



In the Red Crag at Felixstowe I have lately obtained more than a hundred speci- 

 mens, varying in the length of axis from an eighth of an inch to upwards of five eighths, 

 every one of which is in a mutilated condition, but all belonging to this species (what- 

 ever it may be) ; and every one has, more or less, its umbilicus (lacuna), covered over, 

 by apparently, an extension of the left lip of the shell. This extremely mutilated 

 condition evidently indicates that the specimens have been introduced into the Red 

 Crag both at Walton and elsewhere from some older bed, but I have not been able to 

 trace whence. They are very thick and strong shells, more so than any freshwater 

 species in this country. 



[The shell is described by M. Nyst, in his ' Coq. foss. de Beige/ as occurring at 

 Antwerp and Calloo, and as being rare, but he does not there specify in what division of 

 the Upper Tertiaries at these places the shell is found. In his ' Listes des Fossiles des 

 divers Etages,' p. 424, however, he gives it from the Crag jaune (or uppermost crag) 

 only. I do not find it in any of the lists given by M. Vanden Broeck, in his ' Esquisse 

 Geologique,' for the different horizons which he seeks to establish of the beds at, and in 

 the neighbourhood of Antwerp. ED.] 



In the ' Crag Moll.,' vol. i, p. 108, Tab. XI, fig. 2, b, is figured and described a 

 shell from Bramerton, under the name of Paludestrina subumbilicata, which may, I 

 now think, be regarded as the ancestor of the living ventrosa, and it is there stated that 

 in my cabinet was one specimen from the Cor. Crag, the identity of which was given as 

 doubtful in consequence of the Bramerton shell (subumbilicata or ventrosa) being 

 generally considered a freshwater or estuarine inhabitant. This species, however, as 

 well as ulvcB) is capable of living where the water is not quite fresh, and I have 

 lately found in the purely marine Red Crag of Felixstowe a few specimens which appear 

 to me undistinguishable either from the Bramerton shell, or from the living species, called 

 by the British Conchologists Hydrobia ventrosa. If we may depend upon figures and 

 descriptions, there are several continental shells with different names (both generic and 



