CEPHALOrODA. 201 



Hamites, Parkinson. 

 Etymology, hamus, a hook. 

 Example, H. attenuatus (PI. III., Fig. 15). 

 Shell hook-shaped, or bent upon itself more than once, the 

 courses separate. 



Distribution, 58 species. Neocomian — Chalk. South America 

 (Tierra del Fuego), Europe, India. 



b 



Fig. 65, Sutures of Hamites cylindraceus, Defr.* 



The inner courses of this shell probably break away, or are 

 ** decollated," in the progress of its growth. (Forbes.) M. 

 D'Orbigny has proposed a new genus, hamuUna, for the twenty 

 neocomian species. 



Ptychoceeas, D'Orbigny. 



Etymology, ptyche, a fold. 



Example, P. emericianum, D'Orbigny (PL III., Fig. 14). 



Shell bent once upon itself; the two straight portions in 

 contact. 



Distribution, 8 species. Neocomian— Chalk. Britain, France, 

 India. 



Bactilites, Lamarck. 



Etymology, baculus, a staff. 



Example, B. anceps (PI. III., Fig. 13). 



Shell straight, elongated; aperture guarded by a dorsal process. 



Distribution, 17 species. Neocomian — Chalk. Europe, South 

 America (Chili), India. 



BacuUna^ D'Orbigny, 2 species. B. Eouyana. Neocomian. 

 France. Sutures not foliated. 



The chalk of Normandy has received the name of bacalife lime- 

 stone, from the abundance of this fossil. 



* Fig. 65. Space between two consecutive sutures of the right side, from a specimen 

 in the British Museum, a, dorsal line ; b, ventral. Baculite limestone, Fresville. 



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