540 TEST ACE A ATLANTIC A. 



its open and spiral umbilicus, being much in accordance with 

 the latter; nevertheless the fact of its aperture being furnished 

 internally with a quantity of teeth, or plaits, will of course 

 remove it into a totally different section of the genus. The 

 exact number however of these plaits would seem to var} r , — 

 there being according to Sowerby eight of them, and according 

 to Forbes no less than eleven; whilst in a broken and un- 

 matured example which is now before me (and which I ob- 

 tained from out of the loose sandy soil which had filled up an 

 equally subfossilized specimen of the Bulimus auris-vulpina, 

 Chemn.) I cannot satisfy myself of the presence of more than, at 

 the utmost, six, — three of which are (as is acknowledged in all 

 the diagnoses to which I have access) on the ventral paries. 



Considering how unmistakeably defined this singular little 

 species is, as regards its several peculiarities, it is astounding 

 how Forbes, with Sowerby's diagnosis before him, could have 

 republished it, first under the name of //. helenensis, and then 

 under that of Alexandri ; moreover not a single remark con- 

 cerning its affinities is ventured upon, nor is there a syllable to 

 lead us to conclude that it has the slightest connection what- 

 soever with the H. polyodon, — the very title of which, not to 

 mention its habitat, might well have afforded him somewhat of 

 a clue towards its identification. 



The umbilicus of this Patula, apart from its enormous size 

 for a shell which is so diminutive, is further remarkable for its 

 being unusually wide and conspicuous (and, as it were, broadly 

 flattened) at even its extreme apex, or lowest depth. 1 



(§ Acanthinula, Beck.) 



Patula pusilla. 



Helix pusilla, Loiue, Cambr. Phil. S. Trans, iv. 46. t. 5. f. 1 7 

 (1831) 



1 Although there could be little question that Forbes's H. Alexandri is 

 conspeciric with the previously published H. polyodon of Sowerby (for the 

 precise number of the plaits within the curvature of the peristome is clearly 

 variable), it is nevertheless solely on the authority of Pfeiffer that I refer 

 also the helenensis, Forbes, to the latter ; for in his diagnosis of that species 

 Forbes denned the aperture as armed with only four plaits (namely, two on 

 the ventral wall, and two within the outer margin), — instead of the 'eight,' 

 or even 'eleven,' which are said to be conspicuous in the H. polyodon. 

 Nevertheless Pfeiffer seems to have had some sufficient reason for concluding 

 that Forbes's diagnosis, as well as his own, was inaccurate ; for, whilst 

 acknowledging the helenensis in the third volume of his Monograph, he ex- 

 pressly identifies it in his subsequent ones with the polyodon of Sowerby, — 

 adding the observation, in vol. iv., ' Legatur in descriptione : — apertura multo- 

 dentata, laminis 2-3 in pariete aperturali, denticulis usque 8 in margine 

 dextro positis.' It would seem, therefore, that variability as regards the 

 number of its plaits is one of the most distinctive features of this curious 

 little Patula. 



