202 NORTH AMERICAN INDEX FOSSILS. 



less robust; with less distant and less complicated septa; young 

 portion often strongly bent, making an angle of 135° with middle 

 part; venter gently concave, lined by nodes. 

 Pierre of Black Hills. 



352. P. glaber Whiteaves. (Hamites(f) glaher.) Comanchic. 



Section elliptical or ovate, siphonal edge slightly narrower than 



antisiphonal ; surface smooth except for oblique constrictions at 



CO 



Fig. 1467. Ptychoceras mortoni, FiG. 1468. Ptychoceras morioni, suture 



and cross section, X 2. enlarged. (After Meek.) 



distant intervals; septum with three nearly equal saddles on each 

 side, and two divided lobes; siphonal lobe strong. 



Queen Charlotte group of Queen Charlotte Islands, also India. 



353. P. mortoni. (Figs. 1467, 1468.) Cretacic. 



Small ; outer limb impressed over inner ; costse thick and 

 crowded, except in last portion; tubercles on ventral margin of 

 larger limb. 



Pierre of the Upper Missouri, Country. 



CLVII. HELICANCYCLU.S Gabb. (= ( ?) Lindigia Karsten). 



Whorls in contact in early part, and growing in a low, asym- 

 metrical spiral. The ribs are marked by three rows of tubercles 

 on either side of the venter, as in typical Ancyloceras to which 

 it appears to be related. Gerontic stages of a loose ptychoceran 

 form, with recurved crook. Cretacic. 



