244 JOURNAL OF CONCHOLOGY. 



A REPLY TO MR. J. T. MARSHALL'S "FURTHER 

 NOTES ON BRITISH H YDROBI^E;." * 



By EDGAR A. SMITH, F.Z.S. 



(Read before the Conchological Society, July 2nd, 1890). 



I beg to offer a few words in answer to Mr. Marshall's 

 observations. 



In the first place, the author states that three of the four 

 characteristics I have enumerated as separating H. jenkinsi 

 from H. ventrosa are ^'■dearly varietal" . 



r. It seems to me that differences of habit are extremely 

 important, and are not likely to be caused by circumstances 

 which may affect size or colour, such as scarcity of food, or the 

 quality of the water inhabited. They may rather be regarded as 

 inherited characters, not affected by local surroundings. That 

 // ventrosa habitually swims at the surface and H. jenkinsi 

 scarcely ever, indicates a transmitted difference of nature, which, 

 in my opinion, should be regarded as more than varietal. 



2. I fail to comprehend why differences in the colour of 

 the foot and head, and in the greater size and more robust form 

 of the shells, should not in this instance be considered specific. 

 If H. jenkmsl were found in localities where H. ventrosa did 

 not exist, I recognise that the varietal view might be admissible ; 

 but, as both forms occur together, in the same ditches, and 

 consequently subject to the same conditions, these differences 

 have quite another significance. That Mr. Marshall admits the 

 difference in " length and form of tentacles " to be specific, is 

 satisfactory, if not very intelligible. He observes " there can 

 be no doubt that Jeffreys had this shell before him when he 

 described his var. ovata, as the characters of the suggested 

 Z^yd';;,^//'^i'/ are absolutely identical with his detailed description." 



To this I may answer : — 



{a.) If Jeffreys had seen the shell in question, would he 

 not have quoted Plumstead or Beckton as localities, and not 



* Mr. Marshall kindly sent me a proof of his paper. 



J.C., vi., July, 1890. 



