HELIX. 201 



H. MEMBRANACEA Lowe, 1852. PI. 51, figs. 45, 46. 



Imperforate, depressed globose, excessively thin, flexible, pellucid, 

 yellowish or greenish corneous, usually more or less variegated with 

 opaque whitish flecks and reticulations, which sometimes form a 

 stripe at the central keel ; whorls 4, rapidly increasing ; spire low, 

 obtuse; body-whorl acutely carinated at the middle, the carina be- 

 coming obsolete toward the aperture ; not deflected anteriorly ; aper- 

 ture large, broad oval lunar, oblique ; peristome simple, thin, ends 

 scarcely converging; columella simple, arcuate. 



Diam. 10, alt. 6 mill. 



Madeira. 



The excessively thin, easily indented substance of this species will 

 distinguish it from any of its allies. The last whorl is not so acute- 

 ly carinated as in H. webbiana. 



H. cimrn,.v Shuttlcworth. PL f>l, figs. 47-41). 



Imperforate, depressed-conic, very thin and fragile, with a silky 

 lustre, light green, costulate-striate; spire low, conic, apex prom- 

 inent; suture impressed; whorls M, rapidly increasing, convex below 

 th sutures and on base, but concave above and below the prominent 

 peripheral carina; body-whorl large, depressed, carinated to the 

 aperture, not deflected anteriorly, indented at the axis; aperture 

 transversely oval, ungulate at position of carina; peristome acute, 

 membranous; columella deeply, vertically entering. 



Diam. 7, alt. 41 mill. 



Teneriffe and Palnui, (binaries. 



Section VIII. IBERUS Montfort, 1810. 



Helices of the section Iberus are very numerous, both in species 

 and individuals in central and southern Italy, and in Sicily; and 

 curiously enough, there have been a few trans-Mediterranean spe- 

 cies discovered in recent vears. There is great lattitude of opinion 

 concerning the synonymy of the group, arising from the fact that 

 transition forms between many of the "species" render any hard- 

 and-fast lines of demarkation between them wholly arbitrary; and 

 the subject has been still further complicated by a number of diag- 

 noses of tv new species," without figures, each of which' admits of be- 

 inir applied lo several forms. 



The. Sicilian species form a perfect series of gradations between 

 the carinate flattened forms and the globose elevated ones. They 



