SUB-ORDER B 



RHIPIDOGLOSSA 



447 



conical to discoidnl, with wide umbilicus. Spin- fl;itt-n-d or <-vni concave superiorly; 

 whorls angular, the edges sometimes set with nodes (Phymatifer, de Kon.). Outer li]> 

 with emargination at tlie upper angle. Silurian to Tria- : maximum in Carbonift-rou.-. 



FIG. 814. 



I'liKiiHiiliitlti* : rut Hint, Sowb. sp. Carboniferous ; Kildare, Ireland. Discohelix orbis, Reuss. Middle Liaa; 



A, Superior, and B, Inferior aspect. Hinter-Schafberg, Austria. 



Sub-genera : Omphalocirrus, de Ryckholt. Devonian and Carboniferous. Coelocentrm, 

 Zittel. Trias. 



Discohelix, Dunk. (Fig. 8 1 5). Flat, discoidal ; upper side flat or slightly concave, the 

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



Family 6. Stomatiidae. Gray. 



Shell depressed, composed of a few very rapidly widening whorls ; nacreous internally; 

 aperture large. 



With the exception of Stomatia, Helb., and Stomatella, Lamarck, a few rare 

 representatives of which are known as early as the Cretaceous (perhaps also Jurassic), 

 this family belongs to the Recent period. 



Family 7. Turbinidae. Adams. 



Shell turbinate, discoidal, or turreted, nacreous internally. Aperture rounded or 

 oral ; inner lip smooth or with callus, the outer lip never reflected. 

 Operculum calcareous, very thick, convex externally. Ordovician 

 to Recent. 



The extraordinarily abundant recent Turbinidae are dis- 

 tinguished principally by 

 characters of the operculum ; 

 but inasmuch as this is 

 known in but few of the 

 fossil forms, the precise 

 determination of the latter 

 is usually uncertain. It is 



customary, therefore, to 



j , OmptaZotroeMu discus, Sowb. Silurian preserved in place (after 



group under the general Dudley, England. Vi (after Nicholson). Lindstrom). 



head of Turbo such fossil 



turbinate shells with a sub-circular aperture as are not specially distinguished by some 

 other characters. 



Omphalotrochus, Meek (Polytropis, de Kon. ; Oriostoma, Lindstrom non Munier- 

 Chalm.), (Figs. 816, 817). Discoidal or depressed conical, widely umbilicate. Whorls 



Fio. 817. 



n,n t ihit lot rochus globosiis, 

 Sehloth. sp. Silurian ; 

 Gottland. Opt-it-ulnm 



