162 TESTACEA ATLANTICA. 



bicarinata is a more abundant species (or form) than the 

 echinulata, swarming beneath slabs of stone on most of the 

 mountain-slopes of Porto Santo, to which island it would seem 

 (like its immediate allies) to be confined. And so gregarious is 

 it in its mode of life, that I have frequently observed clusters of 

 it under a single block composed of absolutely hundreds of 

 closely-adhering individuals. 



In a subfossil state, the H. bicarinata is decidedly rare ; 

 nevertheless I possess many specimens (collected by myself, 

 chiefly at the Zimbral d'Areia) which I have little doubt are 

 conspecific with it, though their slightly altered fades, from 

 the process of gradual decay to which they have been subjected, 

 renders their identification with the recent type at first sight 

 somewhat dubious. Thus, for instance, the keels of their 

 volutions appear more conspicuous (and the spaces between 

 them, in consequence, more eroded or scooped out) than is the 

 case in the living individuals, and the granulations of their 

 upper surface have in some instances been altogether worn 

 away. Still, there is no shell except the bicarinata to which 

 they can be referred ; and I feel satisfied that they represent 

 the quondam phases of that species, and that they thus far 

 therefore afford presumptive evidence that the H. vermeti- 

 formis (which they almost exactly resemble except as regards 

 their comparatively diminutive stature) cannot properly be 

 looked upon as a mere extinct state of the bicarinata. 



There is however an appreciably larger form of this species 

 (cited in the present catalogue as the ' var. /3. aucta ') to which 

 the subfossil examples 'might perhaps be better referred, in 

 which the upper (or medial) keel is a trifle more horizontal and 

 prominent, and the shell is full 3 lines (instead of only about 

 2-|) across its broadest part which was found in Porto Santo 

 by Mr. Watson, and which I have received from him as the 

 6 recent state of the H. vermetiformis, Lowe.' I am inclined to 

 think, however, that it will be more safely regarded as a highly 

 developed race of the bicarinata 9 from which it differs in 

 scarcely any respect except in its slightly increased stature. It 

 is of course possible that even the subfossilized H. vermetiformis 

 may be in reality but a gigantic extinct phasis of the bicari- 

 nata ; but as it rests upon precisely similar evidence as that for 

 the retention of the H. echinoderma as separate from the 

 echinulata, or as the H. Bowdichiana and Lowei from the 

 punctulata and portosanctana (the 'pros' and 'cons' of which 

 have already been fully discussed), I have thought it desirable 

 to follow Mr. Lowe in treating it as specifically distinct ; and 

 this being the case, it will be sufficient to add that it (i. e. the 

 H. vermetiformis} recedes from the ' var. /3. aucta ' of the //. 



