SUB-ORDER B RHIPIDOGLOSSA 447 
conical to discoidal, with wide umbilicus. Spire flattened or even concave superiorly ; 
whorls angular, the edges sometimes set with nodes (Phymatifer, de Kon.). Outer lip 
with emargination at the upper angle. Silurian to Trias; maximum in Carboniferous. 

Fie. 815. 
Euomphalus catillus, Sowb. sp. Carboniferous ; Kildare, Ireland. Discohelix orbis, Reuss. Middle Lias ; 
A, Superior, and Bb, Inferior aspect. Hinter-Schafberg, Austria. 
Sub-genera: Oimphalocirrus, de Ryckholt. Devonian and Carboniferous. Coelocentrus, 
Zittel. Trias. 
Discoheliz, Dunk. (Fig. 815). 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. 
J 
Family 7. Turbinidae. Adams. 
Shell turbinate, discoidal, or turreted, nacreous internally. Aperture rounded or 
oval ; 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 

Fic. 817. 
Omphalotrochus globosus, 
Schloth. sp. Silurian ; 

customary, therefore, to eee ., Gottland. —  Operculum 
: k > . Omphalotrochus discus, Sowb. Silurian ; preserved in place (after 
group under the general Dudley, England. 1/; (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 

