COELOCENTRUM. 33 



I. Rather large species, the diam. 12 mm. or more. 



a. Remaining whorls 12 in a length of 80 mm.; ribs 



rather strong. C. gigas, p. 33. 



6. Remaining whorls 13 in a length of 54 mm. ; riblets 



numerous and close. C. anomalum, p. 35. 



c. Remaining whorls 9 in a length of 53 mm.; riblets 

 numerous and irregular spirals. Tuxtla, S. E. 

 Mexico. C. nelsoni, p. 35. 



d. Remaining whorls 8% in a length of 43 mm. ; sculp- 

 ture of crowded, delicate lines, no spirals. State of 

 Chiapas. C. pfefferi, p. 34. 



e. Remaining whorls 16-24 in length of 55-72 mm.; 

 thin, fusiform, the riblets very close, fine and weak. 



C. turns, p. 36. 



II. Smaller forms, diam. 6-10, length usually 20-40 mm. 

 a. Ribs of the internal column produced in spines at 

 their junction with the spiral convexity. 



C. astrophorea, p. 45. 

 &. Ribs often serrate but not bearing spines. 



c. Apex retained entire ; whorls 27, length 41, diam. 

 9 mm. C. t. attenuatum, p. 40. 



c 1 . Early whorls lost in the adult. 



d. Whorls short, very closely coiled, about 18 

 in a length of about 38 mm. 



C. arctispira, p. 42. 



d 1 . Whorls short, very convex, 11 in a length of 

 30 mm. C. dispar, p. 44. 



d 2 . Whorls less short, but slightly convex. 



C. tomacella, p. 38; C. t. clava, p. 39; C. 

 fistulare, p. 41. 



C. GIGAS v. Martens. PL 9, figs. 1, 2, 3, 4, 5. 



Shell measuring 21 mm. in diameter and 80 mm. in length 

 (truncate), yellowish-grey, with numerous rather fine, some- 

 what arcuated costulae, of which there are 98 on the whorl 

 before the last, somewhat unequal and irregular, the inter- 

 stices twice or thrice their breadth; spiral striae in the inter- 

 stices very feeble, none on the costulae (fig. 5). Whorls a 



