134 Trans. Acad, ScL of St. Louis. 



the peripheral carina flattened, duplex to complex, and bearing 

 more or less conspicuous nodules, in having the deep parallel- 

 sided anal sinus borne centrally on the peripheral carina, as in 

 Lophiotoma^ and in having a large closely coiled multispiral 

 conically or ogivally pointed embryo, with two or three smooth 

 apical, and one to three longitudinally ribbed basal, whorls. 

 The canal is moderately long, and straight, or nearly so. The 

 American fossil species known to me may be identified by the 

 following characters : — 



Costuliform denticulations of the more strongly elevated peripheral carina, 

 short, varying in length from scarcely a fourth to a sixth or seventh 

 part of the entire length of the whorls 2 



Costulations longer, the peripheral band much broader and generally less 

 strongly elevated, about a third as wide as the length of the wborls, 

 the costules usually becoming gradually less distinct on the larger 

 whorls 16 



2 — Denticulations remaining equally well developed and conspicuous 

 throughout the life of the shell or virtually so 3 



Denticulations only distinct on the young body whorls, becoming gradu- 

 ally more ill defined and obsolete or subobsolete on the larger whorls ; 

 species rather larger in size 12 



3— Denticulations in the form of small longitudinal costules from one of 

 the two peripheral carinae to the other, crossing the intervening feeble 

 depression with but partial interruption 4 



Denticulations feeble, io the form of compressed nodes of the individual 

 peripheral carinae and much broader in a spiral direction than long. . 11 



4 — Fasciolar surface below the subsutural carina deeply concave, then 



rapidly expanding to the strongly elevated peripheral carinae 6 



Fasciolar surface below the subsutural carinule very feebly concave, but 

 obliquely and only moderately rapidly expanding to the less elevated 

 peripheral carinae 7 



5 — Form stout, the apex of the beak distinctly reflexed ; subsutural con- 



cavity with only about two fine revolving threads which are situated 

 at the middle of the concavity ; embryo rather large and well developed, 

 higher than wide, with two or three very small smooth whorls at the 

 summit, followed by three larger whorls which are conspicuously cos- 

 tulose, the riblets of the lowest whorl coarser and generally more 



widely spaced than the others. Red Bluff Eocene arnica Csy. 



Form slender, the beals not reflexed at apex; concave surface below the 

 subsutural carina with a greater number of fine spiral threads, about 

 three on the largest whorl of greniYioa, numerous in rofaedens; embryo 

 smaller but almost similarly formed and sculptured 6 



6 — Peripheral double carina at the middle of the whorls, the denticulations 



rather fine; form very slender, the aperture and canal combined about a 

 third of the total length. Upper Vlcksburg Oligocene.. .rotaedens Con. 



