96 



MAXUAL OF THE MOLLUSCA. 



Shell, spiral, sinistral; whirls separate. 



Bistr.^ 11 sp. Inf. oolite? — chalk. Europe. 

 TuREiLiTES, Lam. 



Etym., turris, a tower, and lithos, a stone. 



Shell, spiral, sinistral ; aperture often irregular. 



Distr., 27 sp. (Bronn). Gault — chalk. Europe. 



The turrUite was perhaps di-branchiate, hy the atrophy of the respiratory 

 organs of one side. M. ;D'Orbigny includes in this genus particular specimens 

 of certain Lias ammonites which are very slightly unsynunetrical ; the same 

 species occur with both sides alike. He also makes a genus {heteroceras) of 

 two tmTUites, in which the last chamber is somewhat produced and recurved. 

 T. rejlexus (Quenstedt, T. 20, fig. 16) has its apex inflected and concealed. 



Fig. 58. Sutures of ha mites cylindraceus, Defr.* 



Hamites, Parkinson. 



Etym., hamus, a hook. 



Ex., H. attenuatus, pi. III., tig. 15. 



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

 rate. 



Distr., 58 sp. Neocomian — chalk. S. America (Tierra del Fuego) — 

 Europe. 



The inner courses of this shell probably break away or are '' decollated" 

 in the progress of its gi-owth (Forbes). M. D'Orbigny has proposed a new 

 genus, hamulina, for the 20 neocomian species. 



Ptychoceras, D'Orb. 

 Etym,., ptyche, a fold. 

 Ex., P. emericianum, D'Orb., pi. III., fig. 14. 



* Fig. 58. Space between two consecutive sutures of the right side, from a speci- 

 men in the Brit. Mus. a. dorsal line. b. ventral. Baculite limestone, Fresville. 



