186 TEST ACE A ATLANTICA. 



are manifestly connected by intermediate grades, and which 

 belong to a type which is essentially a variable one. But no 

 such links have as yet been discovered between the H. Lyel- 

 liana, Albersii and Bulwerii (the second and third of which 

 moreover are associated in the same actual area, and are conse- 

 quently subjected to the same local influences) ; and I do not 

 see, therefore, that we have any right to proceed upon a mere 

 hypothesis (such as we practically decline to apply in so many 

 other instances of a similar nature) and to treat them as other- 

 wise than specifically distinct. 



The H. Lyelliana (which measures about 7^ lines across its 

 broadest part) is a lenticular and strongly carinated shell, the 

 keel being just traceable, in the form of a slightly elevated 

 thread-like sutural line, up the column ; its umbilicus is rather 

 small but spiral; and, with the exception of a few minute 

 granules immediately below the keel, the surface is altogether 

 ungranulated. In colour it is of a pale whitish-yellow beneath, 

 the umbilical area being encircled by a dark castaneous band, 

 between which and the keel there is generally a second one (the 

 two however being sometimes confluent, and occasionally more 

 or less obsolete) ; whilst above, it is of an unequal castaneous 

 brown, mottled with a few irregular transverse yellowish lines 

 and markings (with an obscure narrow castaneous medial 

 fascia), and gradually paler outside the aperture, where there 

 is often also a clear rosy or orange tinge. 



We may regard the H. Lyelliana as representing in the 

 Deserta Grande the Porto-Santan H. Albersii. It is, however, 

 on the average, a trifle smaller and more solid than that species ; 

 its umbilicus is narrower, and more closed-up internally ; its 

 surface has the transverse lines much coarser, but is free from 

 granulations except immediately beneath the keel; the latter is 

 not quite so prominent and tectiform ; its aperture is a little 

 more deflected in front; its base is rather more convex; its 

 keel is traceable as a minute thread-like line up the spire ; and 

 its colour is altogether clearer, brighter, and more variegated, 

 with the darker bands more abruptly and strongly expressed. 



The ' var. /3. gigas ' of this species is not only considerably 

 larger (measuring nearly 9 lines across its broadest part), 

 but it has its keel a little more acute and prominent, though 

 not so traceable (or thread-like) up the spire ; its aperture is 

 not quite so deflexed in front ; and its volutions are 9 in 

 number, instead of only 8. 



Helix Albersii. 



Helix Albersii, Lowe, Ann. Nat Hist. ix. 117 (1852) 

 Bulwerii, ., Pfeiff., Mon. Hel. iii. 161 (1853) 



