200 MAiniAL OF THE MOLLTTSCA. 



ToxocERAS, D'Orbigny. 



Etymology, toxoiiy a bow, ceras, a horn. 

 Example, T. annulare, D'Orbigny (PI. III., Fig. 12). 

 Shell bow-sliaped ; like an ammonite uncoiled. 

 Distribution, 20 S23ecies. Noocomian, Between this and crio' 

 ceras and ancyloceras there are numerous intermediate forms. 



Ancyloceras, D'Orbigny. 



Etymology, anculos, incurved. 



Synonym, Anisoceras, Pictet. 



Example, A. spinigerum (PL III., Fig. 10). 



Shell at first discoidal, with separate whorls ; afterwards pro- 

 duced at a tangent and bent back again, like a hook or crosier. 



Distrihution, 38 species. Inferior oolite — chalk. South America 

 (Chili and Bogota), Euro^DC. 



ScAPHiTES, Parkinson. 



Etymology, scaphe, a boat. 

 Example, S. equalis (PI. III., Fig. 9). 



Shell at first discoidal, with close whorls; last chamber detached 

 and recurved. 

 Distribution, 19 species. Oolite — Chalk. Europe, India. 



Helicoceras, D'Orbigny. 



Etymology, helix {helicos), a spiral, and ce7xis, a horn. 



Example, H. rotundum, Sby. species (PI. III., Fig. 11 — 

 diagram). 



Shell spiral, sinistral ; whorls separate. 



Distribution, 11 species. Inferior oolite? — Chalk, Europe, 

 India. 



TmiRiLiTES, Lam. 



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



Shell spiral, sinistral ; aperture often irregular. 



Distribution, 37 species. Gault — Chalk. Europe. 



The turrilite was perhaps dibranchiate by 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 unsymmetrical ; the same species occur with both 

 sides alike. He also makes a genus {heteroceras) of two turrilites, 

 in which the last chamber is somewhat produced and recurved. 

 T. reflexus (Quenstedt, T. 20, Fig. 16) has its apex inflected and 

 concealed. 





