HARDWICK&S SCIENCE-GOSSIP. 



105 



71 per cent., the general average from all localities 

 being 6SJ per cent. As these statistics clearly prove 

 the fact that the carinated shells form by far the 

 largest proportion, and as it is better to select the 

 prevailing form as the type, I propose, with Mr. 

 Smith's sanction, to consider the carinated form as 

 the typical species, with the non-carinate shells as the 

 variety. The synonym will then be as follows : — 



Hydrobia Jenkinsi. — E. A. Smith. 



Syn. H. ventrosa, var. carinata. — Mai shall. 



Var. A. carinata. — Jenkins. 



= H. ventrosa, var. ovata. — Marshall (non Jeffreys). 



It has been suggested that the carination is merely 

 epidermal ; but, from observations that I have made, 

 I am inclined to believe that the shell itself enters 

 Into the construction of the ridge. The keel and its 

 minute projections, as they appear upon a strongly 

 "keeled specimen, cannot be removed by brushing, 

 and, after being scraped with a pen-knife, the line 

 and ridge can still be discerned with the microscope. 

 Several shells and sections examined microscopically 



Fig. (5.—H. Jenkinsi (E. A. Smith) type. Dorsal and 

 ventral aspect. 



testify that the shell is minutely angulated to form 

 the ridge, the lines of growth being interrupted and 

 bent up towards it. One specimen, a dead shell in 

 my possession, has the brown projections standing 

 up in little tufts from the keel intact and prominent, 

 although every particle of the periostracum has been 

 eroded from the shell ; thus proving that they are of 

 a much tougher nature than the epidermis. 



Having kept the various species in Aquaria for 

 many months, I have come to the conclusion that the 

 Plumstead Hydrobia; differ entirely from H ventrosa 

 in general habits, as well as in their external features. 

 From various experiments which I have made with 

 them, they appear to be more hardy, active, and 

 ■vigorous, they flourish equally well in quite fresh 

 water, or in brackish water from their own habitat. 

 Indeed I have kept them for prolonged periods in 

 bard tap water, containing small quantities of 

 pond-weed, during which they have crawled about 

 with their usual activity. Prolonged emersion of 

 U. ventrosa in tap water has proved fatal to them, 



and they appear very dormant and inactive in fresh 

 pond-water. The former species are also less timid, 

 much more active, and generally prefer crawling 

 about the water-weeds or upon the glass sides of 

 the aquarium, and are seldom seen floating. They 

 also make more use of their long slender tentacles, 

 which seem to perform some important functions for 

 them. 



The Hydrobiaj appear to subsist principally upon 

 decaying vegetable matter. The Plumstead species 

 may be taken in abundance from masses of Chara, 

 and the bright green ribbon-like algae peculiar to 

 brackish water, which I imagine is a species of Ulva:. 

 They often frequent the same ditch, in company with 

 such freshwater congeners as Limncca peregra, L. 

 truncatula, and F/anorbis, as well as with the more 

 marine species Assiminia Grayana. According to 

 Jeffreys several species would seem to have been 

 introduced into this country at various times. Some 

 years ago Mr. Pickering found some shells about two 

 miles below Gravesend (together with a single 

 specimen of Litiopa bombyx), which Jeffreys con- 



Fig. 66.— H. ventrosa (Montagu) type. Crawling and 

 floating. 



sidered closely resembled a Cape of Good Hope 

 species of Hydrobia. Dr. Jeffreys and Mr, Pickering 

 upon several occasions made diligent search in the 

 same spot, but failed to discover any more specimens. 

 From the fact of Litiopa bombyx being peculiar to the 

 gulf-weed, Jeffreys surmised that probably both of 

 these shells were brought into the Thames by some 

 inward bound vessel, attached to the keel, rudder, or 

 chains, and had been carried by the tide into the 

 ditch where Mr. Pickering discovered them. Dr. 

 Jeffreys mentions in "British Conchology" that 

 many years before the late Mr. G. B. Sowerby 

 submitted to him two specimens of H. Ferrussina 

 which Mr. Sowerby said had been found in Hamp- 

 shire. He states that this species, as well as Helix 

 obvoluta (which is confined to the same county in this 

 country) inhabit the greater part of France, and 

 expresses the probability that H. Fermssina may 

 also turn up in the south of England. According 

 to the same author Hydrobia marginata, which now 

 inhabits the south and south-west of France, as well 

 as the Jura and Switzerland, was a very long time 

 ago an inhabitant of our own country, but it is now 



