CANARIAN GROUP. 401 



is satisfactory that the H. argonautula should have been met 

 with by Mr. Lowe and myself, — who, by finding it (in consider- 

 able abundance) at Arguineguin in the south of Grand Canary, 

 were enabled to supply the required data concerning its precise 

 habitat. 



The H. argonavbtula (which measures about 4 lines across 

 its broadest part, and which is composed of about 4^ rapidly 

 increasing volutions), is a thin, sublenticular, and very acutely 

 carinated shell, — the keel (which is irregularly crenulated) 

 being strongly expressed on the upper side on account of a 

 slight groove or erosion alongside it, and being usually traceable 

 up the penultimate whorl as an elevated line adjoining the 

 upper edge of the suture ; its spire is greatly depressed, though 

 with the nucleus a little prominent ; its base is subconically 

 convex, with the umbilicus rather suddenly and deeply scooped- 

 out ; its aperture (which is obsoletely elongate-quadrangular) 

 has the upper and lower portions of the peristome acute and 

 only obscurely connected by a thin intervening lamina ; and its 

 surface is densely sculptured with coarse, irregular, undulating, 

 oblique costate lines. In colour it is of a pale corneous brown 

 (rather paler, and yellowish, beneath, particularly towards the 

 umbilicus), obscurely marbled above with cinereous lines and a 

 few fragmentary patches, and with a narrow band below (seldom 

 two) at a short distance from the keel. 



There is a certain prima facie resemblance between this 

 species and the Madeiran H. tabellata, Lowe ; nevertheless the 

 latter is very much more flattened above, with the whorls 

 narrower and more numerous, and (although quite as acutely 

 carinated) the keel is not shaped-out (or compressed; by an 

 adjoining erosion on the upper side, nor is it visible on the 

 penultimate volution ; its base (although inflated) is not coni- 

 cally-convex ; its umbilicus is narrower ; its aperture is less 

 angular, with the peristome less acute and slightly recurved ; 

 and its surface is less coarsely costate-striate, but studded ivith 

 large granules, as well as more broadly fasciated below. 



Although supposed to be exclusively Canarian, Mousson has 

 lately described (Jahrb. Malah. Ges. i. 81 ; 1874) what he re- 

 gards as a mere phasis of this Helix from Casa Blanca in Morocco, 

 — a fact of considerable importance geographically. But if the 

 Grrand-Canarian form of the species be truly the one which was 

 originally enunciated by Webb and Berthelot (which perhaps, 

 considering the unsatisfactory manner in which it was obtained 

 — namely from amongst dried orchil, — may be open for con- 

 sideration), it is quite clear that it must be accepted as the 

 type, and that consequently the modification from the African 

 continent (whatsoever it may be) should be treated practically 



D D 



