io4 



HARDWICKE'S SCIENCE-GOSSIP. 



is larger and deeper than in the other species. The 

 animal is an active, pretty little creature, with a 

 produced muzzle, and long tapering tentacles which 

 are kept constantly in motion. The shells of the last 

 two species from this locality are generally incrusted 

 with a hard ferruginous deposit, completely envelop- 

 ing the periostracum, but a few examples taken by 

 me are of a clear, pellucid, horn colour. 



Besides the species already described, I have for 

 some years past taken other examples of Hydrobia 

 which cannot satisfactorily be reconciled with either 

 of the above species, and which do not appear to be 

 known to the great continental Conchologists to 

 whom they have been submitted. After a careful 

 study of the living animals, and comparison of their 

 external features with the two species which most 

 nearly resemble them {H. similis and H. ventrosa), 

 Mr. Smith has arrived at the conclusion that it is a 

 new species, which he proposes to name H. Je7ikinsi. 

 Like the other species, they are gregarious, and, from 

 their abounding in ditches in the neighbourhood of 

 Plumstead and Beckton, they may for the present be 

 denominated the Plumstead-Beckton Hydrobia. The 

 shell, which has five volutions, is of a glossy dark 



Fig. 61. — Hydrobia nlva: 

 (Pennant). 



Fig. 62. — //. similis 

 (Draparnaud). 



olive colour, and is larger and more robust than the 

 shell of typical H. ventrosa. It somewhat answers to 

 Jeffrey's description of the variety ovata of //. ven- 

 trosa, and it has been considered by Mr. J. T. 

 Marshall of Torquay to be that variety, which is 

 described in " British Conchology " as follows : — 

 " Var. 3 ovata, shell having a much shorter spire, 

 consisting of only four whorls, which are more 

 swollen than usual, and the last considerably exceeds 

 one half of the shell." I have not at present seen 

 any specimens of this variety with which to compare 

 the Plumstead-Beckton shells ; but as Jeffreys only 

 mentions one locality — viz., Oxwich Marsh, near 

 Swansea — probably it was not very well diffused at 

 that time. But, although the shells may agree with 

 the description of Jeffrey's var. ovata, the animals 

 differ considerably from typical H. ventrosa, both in 

 external appearance and in habits. As a matter of 

 fact, they more closely resemble //. similis, but the 

 tentacles are a trifle longer, and the eyes are placed 

 upon dark-coloured instead of pale prominences. 

 Upon careful examination, Mr. Smith is of the 

 opinion that they " are not absolutely the same, and 

 conchologically the two forms are distinct." The 

 sole of the foot of H. ventrosa, with its central portion 

 of a dark slate-colour, margined with white or stone- 

 colour— described by Mr. Smith as caused by the 



"aggregation of numerous whity brown specks" — 

 is distinctly different from that of the other species, 

 both of which are of a pale grey tint. The animal 

 also is more diminutive, the eyes are smaller and 

 nearly sessile, and the tentacles are shorter, less 

 tapering, blunt at the tips, and are more quiescent 

 when the animal is crawling. They may also be 

 distinguished from the others by their more constant 

 habit of floating or swimming inverted upon the 

 surface of the water. This they exhibit continually 

 in all the aquaria in which I keep them, and if 

 removed to very shallow water, just sufficient to 

 cover them, they have recourse to the same habit. I 

 have sometimes seen the other hydrobke floating, 

 but this occurs but seldom, and not habitually, as in 

 //. ventrosa. Mr. Smith has thus summarised the 

 various distinctions between the Plumstead-Beckton 

 Hydrobia and the other two species in the October 

 number of the "Journal of Conchology": — "It 

 differs from H. ventrosa (1) in habit, (2) length and 

 form of tentacles, (3) colour of the foot and head, 

 and (4) in the greater size and more robust form of 

 the shells. Of the latter, some have simply rounded 

 whorls ; others exhibit more or less of an epidermal 



Fig. 63. — H. ventrosa 

 (Montagu). 



Fig. 64.— H. Jenkinsi 

 (E. A. Smith). 



carination towards the upper part of them (variety 

 carinata of Marshall)." 



"From H. similis it differs (1) in its greater 

 length, higher spire, (2) less pronounced or un- 

 channelled suture, (3) slighter umbilical chink, (4) 

 its tentacles are perhaps the least trifle longer, and 

 (5) the eyes are set on blackish instead of pale 

 swellings." 



The carinated shells to which Mr. Smith refers 

 form by far the largest proportion of the specimens 

 from both banks of the Thames. Strongly keeled 

 specimens exhibit a well-defined line of a darker 

 shade of colour, with little tufted projections at 

 intervals, commencing at the edge of the outer lip, 

 above the periphery, and extending round the body 

 and two preceding whorls, giving the shell a some- 

 what turreted appearance. This carination is more 

 or less apparent in a large majority of shells from all 

 the localities at which I have at present taken them. 

 Out of 2057 shells from the various localities, exam- 

 ined by me with a pocket lens, 1420 specimens 

 proved to be more or less keeled ; a few of these 

 were very young, but the majority had reached the 

 adult condition. The largest proportion of keeled 

 specimens— viz., 85 per cent, on 882 shells examined — 

 were obtained from one locality on the south bank of 

 the river ; specimens from near Beckton produced 



