528 



MOLLUSCA 



PHYLUM VI 



sub-triangiilar, faintly notched ; no umbilicus. Ordovician (Cliazy), and according to 

 Laube, also Triassic. Tyjie, S. angulahts Emmons. 

 Raphistomina Ulr. and Scof. Ordovician. 



Family 6. Stomatiidae Gray. 



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

 aperture large. 



With the excej)tion of Stomatia Helb. and Stomatella Lamarck, a few rare repre- 

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

 family belongs to the Recent period. 



Fig. 865. 



Omphalotrochus discus Sowb. Silurian ; 

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



Family 7. Turbinidae Adams. 



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

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

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



The extremely abundant Recent Turbinidae are distinguished jDrincipally by 



characters of the operculum ; 

 but inasmuch as this is 

 known in but few of the 

 fossil forms, the precise deter- 

 mination of the latter is 

 iLSually uncertain. It is 

 customary, therefore, to groujj 

 under the general head of 

 Turho such fossil turbinate 

 Fi>'- stiii- shells with a sub - circular 



Omphalotrochus glohosus aperture as are not speciallv 



(Schloth.). Silurian; Got- ,. . . -, t ■, ^ , '^ 



land. Opert-uinm pre- distinguished by some other 



.served in place (after characters. 

 Lindstrdiii). 



Omphalotrochus Meek 



(Polytropis de Kon. ; 

 Oriostoma Lindstrijm, 

 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 spinose, and 



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



flattened ; ojierculum 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). Turliinatt; to concial ; aperture nearly circular. Oper- 

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

 nucleus. Silurian (?) to Recent. 



Fici. 8(57. 



Astrnlium (Tlolma) rugo.'^um Linn. Pliocene 

 Pienza, Tuscany. Shell and operculum. 



Fio. S6S. 



AstraUutn {UfanUhi) ilamon Laul)e. 

 Keuper ; St. Cassian, Tyrol. 



