CEPHALOPODA— AMMONOIDEA. 



203 



354. H. aequicostatus Gabb. (Lindigia(f) nodosum Anderson.) 

 (Fig. 1469.) Cretacic. 



Ribs strong, oblique, separated by wide, concave spaces, with 



only growth lines ; nodes strong, rounded ; spire not rising above 



Fig. 1469. Helicancyclus (^quicostatus, top and side views of spiral of a small 

 individual and suture enlarged. (After Gabb.) 



the plane of the outer whorl. Ptychoceran stage, with ribs straight, 

 broader and similarly noded. 

 Chico of California. 



CLVIII. Helicoceras d'Orbigny. 



Ammonoids coiled in a loose, turrilitoid spiral (generally right- 

 handed) ornamented by costse and nodes ; the earliest stages are 

 generally ptychoceran, and the final stages have the retroversal 

 bend of Hamites. Cretacic. 



355. H. stevensoni (Whitfield). (Figs. 1470, 1471.) Cretacic. 



Coiled whorls round, scarcely in contact, with regular, rounded 

 ribs, every other one ornamented by a low node ; a second row of 

 nodes in the last whorl around the open umbilicus. 



Pierre of the Black Hills. 



