From the Niagara Formation. 



75 



Surface marked by fine concentric stria? which follow the direction 

 of the annulations : no longitudinal striae have been noticed. 



This species differs from 0. annulatum in the more gently taper- 

 ing tube, the greater distance of the septa, the low undefined annu- 

 lations, and the fine concentric striae, which are not lamellose, and 

 in the absence of longitudinal striae. 



Nautilus Oceaxus n. sp. 



Shell large, discoidal ; volutions closely coiled but not re-entrant ; 

 umbilicus large and open ; transverse section elliptical, the dorso- 

 ventral diameter being the greater. Shell gradually enlarging. 



Chamber of habitation large ; length twice the greater diameter, 

 the capacity being equal to, or greater than, the entire septate por- 

 tion of the shell ; becoming straight, and free from the inner volu- 

 tions, toward the aperture. Septa regular, two in the space of five 

 centimetres on the ventrum, and five in the same space on the dor- 

 sum. 



The specimens measure from 20 to 25 centimetres in diameter. 



This species resembles N. occidentalh of the Niagara group of 

 Wisconsin, but the form is less gibbous and the septa less distant 

 than in that species. 



Gteoceras abruptum n. sp. 



Shell coiled, rapidly expanding towards the aperture : number 

 volutions about one and a half?, not contiguous. Transverse 

 section broadly elliptical or subcircular ; dorso-ventral diameter 

 the longer. Septa distant, the distance between them becoming 

 gradually greater from the apex toward the chamber of habitation. 

 The last three chambers measure on the ventral side 65 mm., and on 

 the dorsal side about 24 mm. Siphuncle near the ventral side. 



Surface cancellated by longitudinal furrows, about one millimetre 

 wide, Avhich are crossed by finer strong lines of growth. 



The specimen described has had a diameter of about 15 centime- 

 tres. 



This species, in a fragmentary condition, may be distinguished 

 from Nautilus Oceanus with which it is associated, by its smaller 

 size, more distant septa, and more rapidly expanding form. 



