MADEIRAN GROUP. 1C3 



hitherto detected of the latter, in combination with its enormous 

 umbilicus, might seem to render it desirable to refer it to the 

 former, I nevertheless believe that its true affinities are with the 

 Coronaria group. At the same time it has very much in com- 

 mon, also, with the remarkable H. delphinula (the only expo- 

 nent hitherto detected of the section Craspedaria) ; and it is 

 singular that while that species abounds in a subfossil condition 

 near Canical, and has not yet been discovered anywhere alive, 

 there are, on the other hand, no traces whatever of the H. del- 

 phinuloides occurring subfossilized. 



The present extraordinary shell is rather thin and fragile in 

 substance, extremely roughened, perfectly opake, and of a 

 uniform dull pale-brownish flesh-colour varying into a chalky 

 white. It is flattened, rounded, and planorbiform, with its 

 spire greatly depressed, its umbilicus excessively wide and open 

 (being visible spirally to the very apex), with its aperture much 

 deflected, and with its peristome acute, broadly developed, con- 

 tinuous, circular, elevated, and considerably recurved ; and 

 although there is a raised dorsal ridge, which is very conspi- 

 cuous on the basal volution, it has no angular keel (properly so 

 called). 



The sculpture of this curious Helix is very complicated, and 

 not easily to be described : but the upper edge of each whorl is 

 roughened with a series of short, equidistant, transverse ribs, 

 radiating from the suture and extending about a third of the 

 distance across ; beneath which there are a few spiral costse 

 (crossed, or cancellated, by a few finer, remote transverse ones 

 which are a prolongation of the abbreviated basal ribs), which 

 however do not usually fill-up the entire remaining space, but 

 which leave the posterior zone of each volution more or less free 

 and concave. On the ultimate whorl these spiral costse, above 

 the dorsal line, are for the most part only about two in number, 

 the hinder one being the more prominent and constituting a 

 kind of medial thread-like keel ; whilst beneath, the spiral ribs 

 are not only more numerous, but become narrower and more 

 elevated as they approach the umbilicus, — the sides of which 

 they completely crowd, as in the H. delphinula. Like the 

 upper series, these lower spiral ridges are crossed, or decussated, 

 by smaller radiating transverse ones ; and, in addition to all 

 this, there are more or less evident indications on the upper 

 side (at any rate on the basal whorl) of some very oblique and 

 irregular waved lines or subconfluent impressions. 



Helix coronata, 



Helix coronata, Desh., in Fer. Hist. i. 71. t. 69. k. f. 1-4. 

 „ juliformis, Lowe, Ann. Nat. Hist. ix. (1852) 



o 



