CLASS IV 



GASTROPODA 



527 



Btraiiarollina Billings. Canil)ri;ni. OpUleta Vanuxem. Cambrian to Siluriaii. 

 Maclurea Lesciieur ; Maclurina Ulr. and Scof. Ordovician and Silurian. 



Platyschisma M'Coy. Thin - shelled, (l.]ii<>s('d 

 conical, smootli. Unibilicus relatively narruw ; outer 

 lip witli broad sinus. Silurian to Carboniferous. P. 

 helicoides Sowb. Carboniferous. 



Straparollus Montf. (Fig. 862). Turbinate to 

 discoidal, with broad unibilicus. Whorls smooth or 

 witli fine transverse Striae. Silurian to Jura ; especially 

 abundant in Devonian and Carboniferous. 



Phanerotinus Sowb. Like tlie last, except tliat tlie 

 wliorls form an open spiral. Carboniferous. 



Euomphalus Sowb. {Pleuronotus Hall; Schizostoma 

 Bronn) (Fig. 863). Depressed conical to discoidal, witli wide umbilicus. Spire 

 flattened or eveii concave superiorly ; whorls angular, tlie edges sometimes set witli 

 nodes {Phymatifer de Kon.). Outer lip with emargination at the upper angle. Silu- 

 rian to Trias ; maximum in Carboniferous. 



A B 



Fig. 862. 



Straparollus dionysii Montf. 

 Carboniferous ; Vise, Belgiuni. 



Euomphalus catülus (Sowb.). Carboniferous ; Kildare, Ireland. 

 A, Superior, and B, Inferior aspect. 



Fio. 864. 



DiscoJielix orMs Reuss. Middle Lias 

 Hinter-Schafberg, Austria. 



Subgenera : Omphalocirrus de Ryckholt. Devonian and Carboniferous. Coelocentrus 

 Zittel. Trias. 



Discohelix Dunk. (Fig. 864). Fiat, discoidal ; upper side flat or slightly concave, 

 the lower widely umbilicate. Whorls rectangular, with sharp edges. Trias to 

 Oligocene. 



Eccyliomphalus Portlock ; Eccyliopterus Remele ; Helicotoma Salter. Ordovician 

 and Silurian. 



Family 5. Raphistomidae Ulrich and Scofield. 



Gomprising shells intermediate hetioeen the Euomphalidae and Pleurotomarudae^ and 

 regarded as ancestral to these f amilies and the Trochidae. 



Eaphistoma Hall. Shell depressed or completely flattened ; whorls angular above ; 

 umbilicus moderately broad ; outer lip with short notch on the keel. Ordovician 

 and Silurian. 



Euomphalopterus Roemer. Distinguished by its more rounded volutions and 

 excessively developed carinae. Silurian. 



Scalites Emmons, non Conrad. Turbinate, spire only moderately high and 

 acuminate; whorls flattened superiorly, risiut^ sie]. like one above the otlier, sharply 

 angular at the periphery, produced below. Bods w liorl very large, smooth; aperture 



