XXVI GEOGRAPHIC DISTRIBUTION. 



b". Glassy, very thin, with fine obliquely encircling striae, and 

 minutely longitudinally scored when young ; very 

 slender, acutissimum, p. 94. 



a'. With four angles toward the square apex. 



b. 4 bifid or trifid keels towards apex, with fine riblets 



between them, becoming cylindrical and polished toward 



aperture ; length 30 mill., dispar, p. 32. 



b'. A serrate rib at each angle ; white, straightened ; length 



16 mill., 8 times the diam., quadricostatum, p. 33. 



a". With 6 to 13 primary ribs, at least on the smaller half of shell. 



Section not elliptical. 



b. 6 ribs at apex, 12 from middle to aperture, the intervals 

 smooth ; white; length 22 mill., 11 times the diam., 



duodecimcostatum, p. 13. 



b'. 6 ribs at apex, numerous striae soon appearing in each- 

 interval ; length 45-50 mill., 11-12 times the diam., 



pseudosexagonum, p. 23. 



b". 7 ribs at apex, with interstitial riblets anteriorly ; white ; 

 length 14 mill., katowense and cheverti, p. 9.. 



b f ". 8 to 10 primary ribs. 



c. Ribs 8, prominent, intervals deeply concave, with 



a few riblets in adults; white; length 50 mill., 



about 10 times the diam., octangulatum, p. 16. 



G. Ribs 8, narrower, intervals wide, flat ; tinted ;. 



length 48-77 mill., 11-13 times the diam., 



javanum, p. 4.. 



c". Ribs 8-10, low, rounded, obsolete at aperture; 

 length 50 mill., 12 J times the diam., lessoni, p. 8. 

 e'". Ribs 9, rounded, distant, intervals flat ; aperture 

 angular ; length 20 mill., 8 times the diam., 



robustum, p. 12. 



c"". Ribs 10, rather sharp, intervals nearly flat, trans- 

 versely striate ; thin, white, tapering ; length 20 

 mill., about 7 times the diam., 



decemcostatum, p. 8. 



b"". 11-13 strong narrow ribs, intervals with a weak thread 

 or none; length 70 mill., 11-12 times the diam., 



bisexangulatum, p. ] 5. 



a'". 16 angular ribs, smaller ones sparsely intercalated below ; inter- 

 vals clathrate ; tube elliptical in section, clathratum, p. 84. 



