638 



MOLLUSCA 



PHYLUM VI 



Family 12. Tropitidae Mojsisovics. 



Forms usually robust, but ranying from compressed-discoidal to heg-shaped. Body- 

 chamber long. Surface usually highly ornamented with ribs and knots. Septa are 

 goniatitic in some reversionary genera, ceratitic in the most primitive forms known, but 

 mostly slightly digitate. TJiere are no adventitious lobes, and not more than one 

 auxiliary lobe. 



The Tropitidae are derived from the gastrioceran branch of the Glyphioceratidae, 

 witli such forms as Protropites and Columbites as connecting links. 



Siilifamily A. Tropitinae Mojsisovics. 

 Similar to the Anarcestidae in the ephebic stage, but the young frequently have 



volutions Avith highly trapezoidal sections, 

 section of a system of longitudinal 

 ridges and transverse costae. Sutures 

 have deep, narrow ventral lobes divided 

 by siphonal saddles with peculiar trun- 

 cated bases, which are often retained in 

 later stages. Sutures in ejjhebic stages 

 of some forms are similar to those of 

 Haloritinae ; the young have a more or 

 less prolonged coronate stage, and are 



Shells highly ornamented by the inter- 



Fio. 1204. 



Maryarite.i jol'elyi (Hauer). 

 Upper Trias ; Sandliiig, near 

 Aussee, Austria. 



Fir,. 1205. 



Tropites siMu/luliix (Hauer). Upper Trias ; 

 Aussee, Austria. Vi- 



Fk;. 1206. 



Discotropitrn samUingcnsis (Hauer). Up|ier Tiias ; 

 California (after Hyatt and Smitli). 



also keeled on the venter. Aperture narrower and with more ]iointed ventral crests 

 than in the Haloritinae. 



Margarites (Fig. 1204), Tropites (Figs. 1141, C; 1149; 1205), Paratropites (Micro- 

 tropites), Barrandeites, Silbyllites Mojs. ; Discotropites H. and S. (Fig. 1206). Trias. 



