100 ASSIMINEIDtE. 



at the base : inner lip broad, spread on the pillar, which is 

 thickened, but has no umbilicus or chink : opercidum thin, 

 distinctly but irregularly striated in the line of growth ; spire 

 small, sunken, having two or three obscure whorls. L. 0'2. 

 B. 0-15. 



Habitat : Banks of the Thames, between Greenwich 

 and a little below Gravesend (making altogether a dis- 

 tance of about twenty miles), mostly above ordinary 

 liigh-water mark; abundant. It appears to take the 

 place of Hydrobia ulvce, which lives in the upper reaches 

 or brackish water of the Thames. Many years ago I 

 noticed in the collection of the late Mr. T. W. Warren, 

 at Dublin, a specimen of A. Gray ana, which he assured 

 me he had found on the salt-marshes at Portmarnock. 

 Still more doubtful is the only foreign locality, which 

 has been lately given by M. de jNIalzine, in his ^ Essai 

 sur la Faune Malacologique de Belgique,^ viz. " La plage, 

 pres de la frontiere francaise, rejetee par les vagues.^' 

 This writer having also enumerated as Belgian Tellina 

 calcaria, T. similiSf Natica Groenlandicaj Velutina pli- 

 catilis, and other shells of a character equally suspicious 

 as regards geographical distribution, I cannot venture 

 to use his catalogue. This little mollusk, which is not 

 only so restricted in its range, but has such a peculiar 

 organization, is tolerably active, and crawls like a Lit- 

 torina. Mr. Jordan compares its movements, which 

 are very graceful, to the gentle pitching of a vessel. I 

 kept one alive upwards of three weeks, and in fresh 

 water more than twelve houi's at a time. It evidently 

 prefers air to water. While immersed it adhered firmly 

 by its foot to the side of the glass vessel in which it 

 was confined. On two occasions I observed the respi- 

 ratory orifice contracted, and a bubble of air expelled 

 from it. 



