16 HELIX. 



Subsection GONIODISCUS, Fitzinger, 1833. 



Shell depressed, widely umbilicated, periphery angulated. 

 Type H. SOLARIA, Menke. Europe. 



Subsection AMPHIDOXA, Albers, 1850. 



Widely umbilicated, thin, depressed, plane above, convex 

 below, with close, rounded volutions and impressed sutures ; last 

 whorl narrow ; aperture slightly oblique, rounded lunate ; peris- 

 tome simple, acute, margins joined. Type II. MARMORELLA, Pfr. 

 Ins. Juan Fernandez. 



Stephanoda, Albers, 1830, may be placed here as a synonym. 



Subsection MACROCYCLOIDES, Martens, 1867. 



Shell depressed, shining, striate, hyaline, base slightly exca- 

 vated, showing all the whorls, peristome acute, the margins 

 somewhat approaching. Type H. OBSCURATA, Adams and Reeve. 

 East Indies. 

 Subsection TRICHODISCUS, Strebel and Pfeffer, 1819. 



Shell depressed, widely umbilicated, banded, beset with fine 

 bristle-bearing warts; peristome a little expanded. Type H. 

 COACTILIATA, Fer. Mexico, Central America. 



Subsection THYSANOPHORA, Strebel and Pfeffer. 



Shell flat or subconical, widely umbilicated, brown, with longi- 

 tudinal plaits and rows of epidermal fringes ; aperture simple. 

 Type H. IMPURA, Pfr. Mexico. 



Subsection PYRAMIDULA, Fitzinger, 1833. 



Shell pyramidal, minute, costate or strongly striate, umbilicus 

 moderate or narrow. 



Microconus, Strebel, 1880, appears to be synonymous. 

 Type H. RUPESTRIS, Drap. Europe. 



Subsection ACANTHINULA, Beck, 1846. 



Shell perforate, globosely turbinated, with a brownish, pli- 

 cately ribbed, often aculeate epidermis; whorls 4-5; aperture 

 rounded, peristome thin, somewhat expanded, its extremities 

 approaching. 



The buccal plate is transversely and longitudinally striate, its 

 edge slightly indented, with a middle projection. Viviparous, 

 containing embryos in various stages of development at the 



