18 STROBILOPS, CANADA AND UNITED STATES. 



C ^ r. , M ( Sect. Strobilops s. s. 



StrobOo s i Strobilops.... | g^^^_ Eostrobilops. 



^ 1 S.-g. Discostrobilops. 

 I S.-g. Enteroplax. 



Key to Subdivisions of Strobilops. 



1. Parietal callus having a thickened, raised edge, prominent 



where the parietal lamella joins it ; parietal lamellae with 

 smooth or microscopically serrate edges, not nodiferous ; 

 shell thin, carinate. Philippines. 



Subgenus Enteropl^vx, species Nos. 16-19. 

 Parietal callus not noticeably thickened or raised at the 

 edge. (2) 



2. Form conoidal; umbilicus narrow; parietal lamellae gener- 



ally with prickly or rugose nodes. (3) 

 Form subdiscoidal ; umbilicus wide; parietal lamellae with 

 sparsely prickly or smoothish edges, not nodiferous. 



Subgenus Discostrobilops (type ^S'. huhbardi), 

 species No. 15. 



3. Upper sui'face finely striate ; no interparietal lamella. 



Section Eostrobilops (type 8. hirasei), species 

 Nos. 11-14. 

 Upper surface costulate (except in S. morsel, which is 

 nearly smooth) ; an interparietal lamella present. 



Section Strobilops proper, species Nos. 1-10. 

 The species are grouped geographically as follows : 



Canada and the United States, species 1 to 4&, 15. 



Mexico and Central America, species 4c to 7, 15. 



"West Indies, species 15. 



South America, species 8 to 10. 



Japan, Korea and China, species 11 to 14. 



Philippine Islands, species 16 to 19. 



Section Strobilops proper. 

 The shell is troehiform or dome-shaped with the upper sur- 

 face or the ivhole shell ribbed (except in S. morsei). One or 

 two parietal lamellae emerge; deep within, their edges have 

 rugose or prickly nodes (in the Recent species, at least) ; an 



