NOTES ON COMMON SPECIES OF TROCHUS. 459 



Notes on Common Species of Trochus. 



By 

 H. J. Fleitrc and Uliiiiel M. Octtiiig:$, 



University College, Aberystwytli. 



With Plate 28. 



While the present work was in progress a paper on 

 Troclius was published by Randies (10), and stated several 

 results to which our study had also led us. In view of these 

 published results, the present paper has been shortened as 

 far as possible, and includes only some supplementary 

 observations on special points not particularly studied by 

 Randies. 



Our observations, in the main, confirm those he has 

 described. We find, for example, the pericardial communi- 

 cations of the kidneys just as he has stated, and are thus led 

 to the belief that the Rhipidoglossa possess, typically, a 

 pericardial canal for each kidney, the gonad communicating 

 with the pericardial canal of the right kidney. 



Randies rightly refers to the unsatisfactoriness of Pilsbry's 

 subdivision of the old genus Trochus or the family Trochidee 

 from the anatomical point of view, and we have found the 

 two commonest species of Trochus of interest in this connec- 

 tion. In Pilsbry's work Trochus lineatus. Da Costa, often, 

 and perhaps better, styled T. crass us, Montagu, becomes 

 Monodonta crassa, Montagu, and belongs to the group of 

 the Trochininge. In discussion we shall use for it the name 

 T. crassus, Montagu. Pilsbry makes T. umbilicaris. 



