jOtfRNAL OP CONCriOLOGY 3^5 



NOTICE OF A MONSTROSITY OF BYTHINIA 

 TENTACULATA. 



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

 Zoological Department, British Museum. 



PI. ii, fig. 27. 

 It is a recognised fact that most shells are subject to more or 

 less variation in many respects, and that the limits of variation 

 and the passage into forms, which may be called monstrous, are 

 not clearly defined. 



Although several varieties of Bythinia tentaculata have 

 been indicated by several authors I have not been able to 

 discover any mention of a monstrosity of this species. 



In 1830 Menke named four varieties : — (a) ventricosa \ (b) 

 producta ; (c) ^or^a (a. major, b. viinor) ; (d) obtusa. Ten years 

 later Garnier created a fifth, var. curta \ Morch has termed a 

 sixth form, var. gigas ; Jeffreys has designated two others, var. 

 decoUata and var. excavata respectively, and it is possible other 

 authors may have employed other equally useless varietal names. 



All these terms have reference to variation in form, and 

 the specimen under consideration also presents an extreme 

 deviation from the normal contour of the species. The spire 

 is remarkably depressed, the apex being elevated not more than 

 a twenty-fourth of an inch above the body-whorl. The volutions 

 are very narrow, convex, and involute above so as to produce a 

 remarkably channelled suture. The last whorl is broad at the 

 upper part and obtusely angled at the periphery, producing 

 somewhat squarish aspect. The aperture is altogether of an 

 abnormal form, and being much narrowed above has an elongate 

 pyriform appearance. 



The tout ensemble of the shell is so very unlike the typical 

 form of the species that it was pronounced by two conchologists 

 to whom I submitted it (not informing them of its locality) to 

 belong to the BiillidcB ! In texture and colour, however, it is 



