58 HELIX-MACROON. 



characterized by the relatively great size of the egg, and the corre- 

 spondingly large embryonic or nuclear shell, which is in most of the 

 species from one-fourth to over one-third the total diameter of the 

 adult shell. It is in most cases sculptured differently, more regu- 

 larly and elaborately, than the post-embryonic portion of the shell. 

 The termination of the embryonic or nuclear shell is distinctly 

 marked by the change of sculpture, or color, and by an oblique 

 streak or wrinkle of the surface. The adult shell is either imperfor- 

 ate or umbilicate ; but the umbilicus when open, does not penetrate 

 deeper than the last whorl. The contour of the adult shell varies 

 fromdepressed^globose, heliciform, to elevated and bulimiform. The 

 various modifications of shell and nucleus will be discussed more 

 fully under the several sectional heads. 



I have offered a new name because the group is wholly new, both 

 in the collocation of its contents and the characters upon which it is 

 founded. 



Four well-marked sections may be recognized : 



(1.) HELICOPHANTA, large Madagascar shells, with a distinct line 

 marking the junction of the nucleus with the post-embryonic growth, 

 the latter consisting of one and a half whorls or less ; form varying 

 from heliciform to bulimiform ; whorls 4 to 5, very rapidly widen- 

 ing ; lip expanded or reflexed, narrow ; the columellar margin 

 somewhat dilated at its insertion at the axis. 



(2.) PANDA, globose-bulimoid shells of great size and variegated 

 coloration, the nucleus not marked off from the after-growth nor 

 different from it in any way ; whorls 4? or less, rapidly widening ; 

 lip simple, not expanded, dilated and reflexed on the columella. 

 The two species inhabit Australia. 



(3.) ACAVUS, a Ceylonese group of brightly colored species ; the 

 junction of the nuclear and post-embryonic whorls not strongly de- 

 fined generally, but visible ; whorls less than 5 in number, rapidly 

 increasing; lip broadly expanded, the columellar margin long, 

 obliquely descending, very broadly flattened and adnate to the base. 



(4.) STYLODONTA having a brown helicoid shell with about 5? 

 slowly widening whorls, the nucleus differently sculptured and easily 

 distinguishable from the post-embryonic growth, the latter consist- 

 ing of more than two whorls ; lip expanded or reflexed ; the col- 

 umella very short, vertical, convex or toothed. Habitat, Seychelles 

 Islands. 



