596 NORTH AMERICAN INDEX FOSSILS. 



\. Spire slightly elevated, shoulder deeply concave. 



LV. Helicotoma. 

 W. Keel marginal, often sharp and high, forming a nearly vertical 



blade, spire deeply depressed LIV. Eccyliopterus. 



20*. Keel with distinct slit band L1II. Ophiletina. 



16. Notch only on outer margin of upper surface, no keel, with raised line 

 on upper surface, interrupting lines of growth ...XXVI. Raphistoma. 



16. Without notch or band, but with strong peripheral carina; depressed- 



conical XXVII. Raphistomina. 



H. Shell with aperture notched anteriorly or drawn out into a canal of greater or less 

 length. 

 VIII. Shell turreted, long and slender, aperture less than half the greatest length 

 of shell, rarely its equal 17. 



17. Aperture without expanded lip, notch short ....21*. 



21*. Aperture modified by sharp folds c / . 



c / . Aperture more or less oblique 9999- 



9999. Folds always on columella, generally on outer lip as 



well CXXXI. Nerinea. 



9999. Fold on outer lip, sometimes also on columella. 



CXXXII. Nerinella. 

 c / . Aperture elongate axially ; folds on columella ; notch faint. 



5°- 



50. Spire elevated, smooth or with ribs CLXXXIV. Mitra. 



50. Spire short, shell oval, surface smooth. 



CLXXXIII. Marginella. 



50. Spire short, surface ribbed CLXXXIVA. Conomitra. 



21*. Aperture unmodified by folds d / . 



d / . Aperture oblique, canal oblique 51. 



51. Surface ornamented CXXXIV. Cerithium. 



51. Surface smooth CXXVIII. Melanopsis. 



d / . Aperture oval to quadrilateral 52. 



52. Outer lip entire CXCII. Terebra. 



52. Outer lip with faint notches CXXV. Glauconia. 



d / . Aperture elongate, ovoid LXXXV. Fusispira. 



d / . Aperture elongate, narrow 53. 



53. Outer lip entire ee / . 



ee'. Surface smooth LXXXIV. Subulites. 



ee / . Surface cancellated by ribs and spirals. 



CXXXIII. Bitlium. 



53. Lip with notch or slit ff / . 



ff'. Notch at suture CXCV. Mangilia. 



ff'. Notch below suture CXCIV. Drillia. 



17. Aperture with outer lip expanded (often broken away or not shown in 



immature individuals) 22*. 



22*. Expansions wholly adhering to spire which may be mostly covered. 



CXXXVI. Calyptrophorus. 

 22*. Expansion free or only partly adhering to spire, which may never- 

 theless be concealed by it e'. 



e'. Expansion simple, free, and blade or wing-like, sometimes di- 

 vided, anterior end drawn out into canal. 



CXXXV. Anchura 



