872 TJSS /'. I ( A'. 1 A TL. I XTK '. i . 



there is not a feature on which their various claims as (so-called) 

 'species' has been -apposed to rest which does not seem to me 

 to be totally unreliable and fluctuating. Thus the H. gemi/nata 

 of Mousson, which in its normal condition is larger, more solid, 

 and more depressed than the typical piscina, with its sculpture 

 perhaps a little coarser, its perforation entirely closed, and its 

 colour peculiarly dark and lively, passes by such imperceptible 

 gradations, in all these several particulars, into the usual aspect 

 of the pisana proper, that many hundreds of examples which 

 are now in my possession (from different islands, and districts, 

 in the Group) leave me in complete uncertainty as to which of 

 the supposed ' species ' they should be referred ; and I do not think 

 that it would be possible to decide positively whether they are 

 the true piscina (as limited by Mousson) or the geminata. I 

 have no hesitation therefore in regarding the H. geminata as a 

 mere geographical development of the pisana, — perhaps some- 

 what characteristic of the Canarian archipelago, but neverthe- 

 less assuredly passing into the ordinary Mediterranean type by 

 every conceivable shade of intermediate link. And similar obser- 

 vations may apply to the H. Grasseti, Tarnier (=planata (pais) 

 W. et B., nee Chemnitz), from the Isleta of Grand Canary, — 

 which retains all the essential characters of pisana proper, ex- 

 cept that its spire is remarkablv depressed, its keel is more 

 acute, its perforation is nearly concealed, and its decussating 

 stria? are quite as coarse as in the var. geminata. 1 



In its more typical aspect I have taken the H. pisana 

 (which occurs likewise in the Azorean and Madeiran Groups) in 

 Lanzarote, as well as on the little adjacent island of Graciosa, 

 in Grand Canary (principally below Tafira), and in Teneriffe 

 (about Laguna and Sta. Cruz ). The examples from Fuerteven- 

 tura (where Mousson records the species as having been found 

 by Hartung in even a subfossil condition) are more emphatically 

 referable to the var. geminata than those from any of the other 

 islands, — being on the average extremely large, solid, and 

 deeply coloured, with their perforation seldom otherwise than 

 quite closed up. The Teneriffan ones are usually somewhat 

 smaller, and are often (as regards their umbilicus and sculpture) 

 intermediate between the geminata and the type ; certain of 

 them also, from Laguna and near Orotava, being of a uniform (and 

 comparatively constant) buff hue, with but small and insignifi- 

 cant markings superadded. Whilst my Gomeran individuals 



1 I am not indeed altogether sure that even the Lanzarotan H. impitgnata, 

 Mousson, would not be treated by certain monographers as an extreme 

 development of the H. pisana, — its var., or status, ' subgeminata,' having a 

 good deal in common with the ' var. Grasseti ' of the pisana ; nevertheless, as 

 this is more doubtful, I will not attempt to open up the question. 



