144 SMITH : ON BRITISH HYDROBIyfi. 



in front ; head rather protuberant ; snout long and ridged trans- 

 versely.; tentacles filiform, with black and grey rings ; eyes on 

 very short stalks, placed a little behind the outer base of the 

 tentacles ; foot cleft in front and rounded behind." 



This description does not suit the specimens from Erith 

 which I have observed. They were pale grey all over, excepting 

 a slight blackish colour on the sides of the body and on the 

 head in front of the tentacles ; head scarcely protruded beyond 

 the anterior margin of the aperture of the shell, finely annulated; 

 tentacles slender, only slightly tapering, not pointed at the tips, 

 uniformly pale, not ringed ; eyes black, scarcely raised on pro- 

 tuberances, situated at the outer bases of the tentacles ; foot 

 small, short, produced on each side in front, almost forming 

 falcate corners, rounded posteriorly, sole pale, transparent, with 

 a stripe down each side consisting of numerous aggregated 

 whitey-brown specks. 



Contrasting this description with that given by Jeffreys a few 

 differences are noticeable. When crawling the specimens which 

 I have observed protruded the proboscis only a very little beyond 

 the shell, and it certainly could not be described as " rather 

 protuberant," nor should I consider the snout "long." I could 

 find no " black and grey rings " on any of the tentacles, and the 

 eyes appeared almost sessile and not " on very short stalks." 



My notes on the animal oi H. similis are as follows: — Foot 

 pale, produced on each side in front, rounded behind ; head and 

 proboscis blackish above, finely ringed transversely, considerably 

 protruded beyond the shell ; tentacles* slender, finely tapering, 

 semi-transparent ; eyes on slight cream-coloured prominences or 

 swellings. The latter feature is also noted by Forbes and 

 Hanley in their description of this species. 



The animal of H. jenkinsi appears to be remarkably similar 

 to that of H. similis both in external appearance and habit. The 



* The tentacles of all the three species exhibited microscopic lateral 

 processes in a greater or less degree. These may be " vibratile ciha " as 

 described by Jeffreys in connection with H. idva;, or "vibrilkie" mentioined 

 by Haldeman (Freshw. Univ. Moll., U. S., Turbidre p. 6). 



J.C., vi., Oct.. iS8o. 



