STROBILOPS OP SOUTH AMERICA. 39 



clearly those lamellse by seeking it. Under an ordinary lens 

 these lamellae show also in S. salvini the repeated swellings 

 described by Morse. In fragments of S. lahyrintJiica from 

 Florida, examined for comparison by myself and Dr. Hilgen- 

 dorf, under a higher magnifying power, the swellings appear 

 to be somewhat less regular, and composed of more scattered 

 and shorter points than in the said figures." 



South American Species. 



Strohilops morsel and 8. hraziliana appear to be closely re- 

 lated to species of Central America and Mexico, with which 

 they agree in internal armature. 



By its smooth surface S. morsei is unique, but some speci- 

 mens show very weak traces of ribs, showing descent from a 

 ribbed ancestral stock. 



8. helleri is a very distinct species, possibly forming a sep- 

 arate subgenus, but I have not opened the single specimen 

 found; its internal structure is not known. 



Key to South American Species. 



1. Shell elevated, trochiform, of 5I/2 to 6 whorls, the last with 



angular periphery and weakly convex base ; umbilicus 

 narrow, contained 11 to 13 times in the diameter; diam- 

 eter about 2.5 mm. (2) 

 Shell rather low, of 4I/2 whorls, with dome-shaped spire, 

 carinate periphery and strongly convex base ; umbilicus 

 large, contained about 4 times in the diameter ; diameter 

 about 3 mm. Galapagos Islands. ;8'. helleri, No. 10. 



2. Surface nearly smooth. Venezuela. S. morsei, No. 8. 

 Surface strongly ribbed. Brazil, ;S^. hrasiliana, No. 9. 



8. Strobilops morsei (Dall). PI. 6, figs. 4, 5, 6. 



The shell is trochiform with nearly straight lateral outlines, 

 obtuse apex, strongly angular periphery and weakly convex 

 base, perforated by a very small umbilicus, contained between 

 12 and 13 times in the diameter. The whorls are weakly 

 convex. Dead but rather fresh specimens are cinnamon- 

 colored without much gloss; nearly smooth, but there are 



