CLASS IV 



GASTROPODA 



.49 



loith short canal or shallow notch. Golumella and Ups with strong folds, contimious 

 throughoid the eniire length of the spire. Outer lip thin, posteriorly luith ßssure-like 

 incision, which leaves a small slit-hand immediately heneath the suture on all the whorls. 

 Marine. Trias to Cretaceous. 



Aptyxiella Fisch. (Äptyxis Zittel, non Troschel). Turreted, very slender, im- 

 perforate. Aperture qiiadrangular ; inner and oiiter Ups witliout folds ; columella 

 somewhat thickened. Trias to Upper Jura. 



Trochalia Sharpe {Gryptoplocus Pict. and Camp.) (Fig. 972). Turreted to 

 pyramidal, usually smooth and imperforate. The inner lip only has a strong, simple 

 ibid. Jura and Cretaceous. 



Nerinella Sharpe (Pseudonerinea Loriol). Turreted, imperforate. Outer lip and 

 sometimes also the columella with a simple fold. Jura. 



Nerinea Defr. (Fig. 973). Turreted or pyramidal, usually imperforate. Columella 

 invariably, and inner and outer lips generally, with simple folds. Jura and Cretaceous ; 

 maximum in the Coral-Rag (Upper Jura). 



Ptygmatis Sharpe (Fig. 974). Like the last, except that the folds on both lips 

 and the columella are complicated by second- 

 ary constrictions and branchings. Jura and 

 Cretaceous. 



Itieria Math. (Fig. 975). Elongate-oval, 

 usually umbilicate. Spire short, sometimes 

 insunken, Body whorl very large, more or 

 less enveloping the preceding. Columella 

 and both lips with folds. Jura and Cre- 

 taceous. 



Family 17. Cerithiidae Menke. 



Shell turreted; aperture elongated oval, or 

 quadrilateral, anteriorly with short canal. 

 Outer lip often thickened and reflected, or thin 

 and sharp. Columella sometimes with one 

 or tivo folds. Operculum horny, spiral. 

 Marine and hrackish water. Trias to Recent. 



Fio. 974. 



Ptygmatis pseudo- 

 bruntrutana Gem- 

 mellaro. Tithonian; 

 Inwald, Carpathia. 

 Vertical section. 



Fig. 975. 



Itieria staszycii Zeuschner. 

 Tithonian ; Inwald, Car- 

 pathia. 



More than 1000 living, and about 500 

 fossil species are known, the latter being most numerous in the Eocene. The earliest 

 forms are usually of small size, and have a nearly entire peristome. 



Gerithinella Gemm. (Fig. 976). Shell turreted, slender. Whorls numerous, flat, 



ornamented with spiral ribs or rows of small nodes. 

 Aperture quadrilateral, with very faint canal. 

 Jura. 



Cryptaulax Täte (Pseudocerithium Cossmann). 

 Small, turreted. Whorls with spiral ribs or rows 

 of nodes and transverse folds. These last usually 

 run continuously in a somewhat oblique direction 

 from one whorl to the next. Aperture oval or 

 quadrilateral, with scarcely perceptible canal. 

 Trias and Jura. 



Ceritella Morris and Lyc. (Fig. 977). Trias 

 and Jura. Fibula Piette (Fig. 978). Trias to 

 Cretaceous. Pseudalaria Huddlest. ; Ditretus Piette. Jura. 



Exelissa Piette (Fig. 979). Very small, turreted ; whorls with strong, continuous 



Fi(!. 976. 



Cerithinella aiinata 

 Goldf. Torulosus 

 Beds (Middle Jura) ; 

 Pretzfeld, Franconia. 



Fig. 977. 



Ceritella conica 

 Morris and Lyc. 

 Great Oolite ; Min- 

 chinhamptoii, Eng- 

 land. 



