96 MANUAL OF THE MOLLUSCA. 



Shell, spiral, sinistral ; whirls separate . 



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

 TuKKiLiTES, Lam. 



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



Shell, spiral, sinistral ; apertm-e often irregular. 



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



The turrilite was perhaps di-hranchiate, by the atrophy of the respiratory 

 organs of one side. M. [D'Orbigny includes in this genus pai'ticidar specimens 

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

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

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

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



Fig. 58. Sutures of hamites cylindraceus, Defr* 



Hamites, Parkinson. i 



Etym., ha.mus, a hook. ^ \ 



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



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

 rate. 



Disfr.^ 58 sp. Neocomian — chalk. S. America (TieiTa del Enego)— 

 Europe. 



The inner com'ses 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 20 neocomian species. 



Ptychoceras, D'Orb. 

 Etym., ptyche, a fold. 

 E.X., 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. 



I'l 



