528 



MOLLUSCA 



PHYLUM VI 



ßub-triangular, faintly notched ; no umbilicus. Ordoviciaii (Chazy), and according to 

 Laube, also Triassic. Type, S. angulatus Emmons. 

 Raphistomina Ulr. and Scof. Ordovician. 



Family 6. Stomatiidae Gray. 



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

 o,perture large. 



Witli tlie exception of Stomatia Helb. and Stomatella Lamarck, a few rare repre- 

 sentatives of wliicli are known as early as tlie Cretaceous (perliaps also Jurassic), tliis 

 family belongs to tlie Recent period. 



Fig. SC5. 



Omphalotrochus discus Sowb. Silurian ; 

 Dudley, England, i/j (after Nicholson). 



866. 



Family 7. Turbinidae Adams. 



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

 oval; inner lip smooth or with callus, the outer lip never reßecied. Operculum cal- 

 careous, very thick, convex externally. Ordovician to Recent. 



The extremely abiindant Recent Turbinidae are distinguished principally by 



cliaracters of tlie operculum ; 

 but inasmuch as tbis is 

 known in but few of tlie 

 fossil forms, tlie precise deter- 

 mination of tlie latter is 

 usually uncertain. It is 

 customary, therefore, to group 

 under the general head of 

 Turbo such fossil turbinate 

 Shells with a sub - circular 

 Omphalotrochus gioiosus aperture as are not speciallv 



(Schloth.). Silurian; Got- ,. ^. • i n i , 



nd. Operculum pre- aistinguished by some otlier 



served in place (after pItj, rnptpr« 



Lindströin). cuaracters. 



Omphalotrochus Meek 



(Polytropis de Kon. ; 

 Oriostoma Liiidström, 

 non Munier - Chalm.) 

 (Figs. 865, 866). Dis- 

 coidal or depressed 

 conical, widely umbi- 

 licate. Whorls round, 

 ornamented with 



raised longitudinal 



keels. Operculum extremely thick, fiat internally, conical externally, multispiral. 



Ordovician to Carboniferous ; especially abundant in Silurian. 



Astralium Link (Figs. 867, 868). Turbinate; whorls rough, often spinöse, and 



usually keeled. Aperture depressed, witli disconnected margin. Base more or less 



flattened ; operculum calcareous, thick, flat internally, spirally coiled, and with very 



eccentric protoconch. Trias to Recent. 



Subgenera: Bolma Risso (Fig. 867); Pachypoma, Lithopoma, Uvanilla (Fig. 868), Guil- 

 fordia Gray ; Calcar Montfort, etc. 



Turho Linn. (Fig. 869). Turbinate to concial ; aperture nearly circular. Oper- 

 culum calcareous, thick, flat internally, externally convex, multispiral, with sub-central 

 nucleus. Silurian (?) to Recent. 



Fig. 867 



Astralium (Bolma) rugosum Linn. Pliocene : 

 Pienza, Tuscany. Shell and operculum. 



Astralium (Uvanilla) damon Laube. 

 Keuper ; St. Cassian,Tyrol. 



