2 26 NOTES ON THE MOLLUSCA OF THE THAMES ESTUARY, 



in his opinion that the new Hydrobia was a distinct species, as, 

 putting aside the difference in the form and contour of the shell, the 

 tufts and carination of a large majority of the specimens, &c., the 

 habits and external appearance of the creatures were quite character- 

 istic. Mr. Marshall frankly acknowledged in his " Further Notes on 

 British Hydrobise " (Journal of Conchology, vol. vi., p. 224), that 

 having always taken Jeffreys for granted, he " had not examined the 

 animal." I at once sent him living Hydrobiae for comparison. About 

 this time a correspondent of mine sent me a solitary shell of the true 

 variety ovata, Jeffreys, of H. ventrosa (which had been authenticated 

 by Mr. Marshall), affording me the opportunity of comparing it with 

 specimens oi H.jenkinsi, from which it differed considerably. 



The examination of the living Hydrobiae and the discovery of the 

 real variety ovata seemed to convince Mr. Marshall, and soon after- 

 wards he subscribed to Mr. Smith's opinion that the Plumstead- 

 Beckton Hydrobia was entitled to rank as a new species. From this, 

 I conclude that the variety ovata of H. lenirosa is exceedingly rare, 

 as otherwise comparison of the two shells would have settled the 

 affair at once. To me it has often been a matter of deep regret that 

 the splendid collection of Dr. Jeffreys, containing his types, was ever 

 allowed to go out of this country. 



The carination and little tufts upon many of the shells of H. 

 jenkinsi are very peculiar, and form one of the features by which we 

 can readily distinguish them from allied species. An examination 

 with a pocket lens of between two and three thousand shells, from 

 various places, proves that by far the larger proportion show more or 

 less traces of the carination, although but few specimens show these 

 processes in perfection. Amongst the marine and brackish-water 

 shells of the Antipodes there are quite a number of species of 

 Hydrobia which are either keeled and tufted, or else possess a number 

 of delicate hair-like processes, running spirally around the body and 

 preceding whorls just upon or above the periphery. Several New 

 Zealand species are strongly keeled, and the shells are either tufted 

 or sericeous. Potamopyrgos corolla, Gould, is strongly carinated 

 with a number of very short bristles, proceeding from the keel, and 

 the very beautiful shells of P. cumingiana, Fischer, have a number 

 of long silky processes. P. antipodium, Gray, appears generally to 

 be ecarinate and without tufts or hairs, although a few tufted 

 specimens may occasionally occur. This species appears most 

 nearly to resemble H. jenkinsi, and one variety might easily be 



