538 TEST ACE A ATLANTIC A. 



The excessive flatness of its spire, the whorls of which (even 

 though the examples from which Sowerby drew up his diagnosis 

 were subfossilized ones) appear to be more or less transversely- 

 dappled ' with irregular ferruginous rays,' in conjunction with 

 the comparative convexity of its base, and its very small and 

 well-nigh closed-up umbilicus, will serve additionally to distin- 

 guish the P. bttamettata from everything else with which we 

 are here concerned. Its extreme breadth seems to be nearly 4 

 lines, but its altitude only about 1^. The following is Sowerby's 

 diagnosis of it : 6 T. orbiculato-depressa, spira plana, anfractibus 

 senis, ultimo subtus ventricoso, superne angulari ; umbilico 

 parvo ; apertura semilunari, superne extus angulata, labio ex- 

 terno tenui ; interne plicis duabus spiralibus, postica majori.' 



Patula biplicata. 



Helix biplicata, Sow., in Darwin's Vole. Isl.. Append., 158 



(1844) 

 Melliss, St. Hel. 121 (1875) 



Habitat in calcareis, versus borealem insulae ; semifossilis. 



The only example which I have seen of this very minute 

 Patula (which measures about 1^ lines across its broadest part) 

 was obtained by myself from out of the calcareous soil which 

 had filled-up the aperture of an equally subfossilized Bulimus 

 Darwinianus ; but its characters are so decided that there is 

 no possibility of falling into error as regards the identification. 

 It appears to be quite distinct from the P. bilamellata, for 

 not only is its form different (the spire being much less flattened, 

 and the posterior edge of each volution not angular), but its 

 umbilicus also is considerably larger and more open. Like 

 that species it has two spiral plates, the upper one of which is 

 rather the most elevated, on the ventral paries ; and it is trans- 

 versely sculptured with very powerful and well-defined costse. 



From the polyodon, Sow. ( = Alexandri, Forbes) the pre- 

 sent Patula may be known by, inter alia, its less flattened 

 spire, and more remote and raised ridges (which are continued, 

 though perhaps not very coarsely so, on the underside of the 

 shell), by its relatively much smaller umbilicus, and by its 

 having no appearance of plaits inside the outer lip. 



Patula Cutteri. 



Helix 'Cutteri, Pfeiff., Mai. Blatt. 206 (1856) 

 Id., Mon. Hel. iv. 155 (1859) 

 Melliss, St. Hel. 1 20 (1 875) 

 Habitat regiones editiores sylvaticas ; ad c Diana's Peak ' a 

 Dom. Cutter detecta. 



