ORDER III 



TELEODESMACEA 



405 



depressions (Fig. 732, x, x) next tin- sinus \\viv shown l>y IVtlx. to ha\v lieen.the seat 

 of a ligmentary connection between the valves; the adductor scars (a, a') ivsi ml,].- 

 those of Radiolites. Widely distributed in tin- Middle and Upper Cretaceous. 



The supposed genera IHpilidia, Birostrites, and Jodamia are based on internal. 

 casts of Radiolites. The visible submersion of tin- ligament in some Radiolites enable.- 

 us to understand how the stages shown by Hippurites have arisen. 



Family 14. Hippuritidae. Gray. 



Shell substance of two layers, the external porous, grooved, and punctate ; the inner 

 lacunary and prismatic; exterior with sutures corresponding to an "anal" and 

 " branchial " inflection, and sometimes with a ligamentary suture ; clithrum formed of 

 two processes in the free valve, the adductors attached to myophores ; fixed valve with one 

 thin laminar process ; the adductor scars excavated, the anterior adductor duplex, forming 

 distinct scars. Cretaceous. 



Hippurites, Lam. (Figs. 733-737). Lower valve cyliudro-conic, sometimes a metre 

 in length, attached by the apex, smooth or longitudinally ribbed, with three furrows 



Fio. 733. 



Hijifii rites Gosaviensis, 

 Douv. Upper Cretace- 

 ous ; Gosau Valley, 



Austria. V-j. 



FIG. 734. 



Hippurites Oppeli, Douville. Nefgraben, near Russ- 

 bach, Salzburg. A, B, 0, Impressed lines bounding 

 convex vertical areas (columns) corresponding to the 

 region of the hin^e. i/ 2 . 



FIG. 735. 



H 1/11111 rites organimns, 

 Montf. Vertical section 

 of a valve below the 

 living chamber, show- 

 ing the septa ami int'T- 

 septal cavities of the 

 middle layer, l/i- 



bounding two " columns," or columnar areas, extending from the apex to the upper 

 margin (A, B, C). Upper valve depressed, conic, with sub-central umbo, usually with 

 two round or oval foramina ; outer surface showing pores, the apertures of short canals 

 which join larger canals radiating from the beak. The thick outer layer of the lower 

 valve is usually brown-coloured and made up of thin horizontal strata, which are in 

 turn composed of small vertical prisms. The white inner layer is porcellanous, and 

 sometimes contains vacant spaces in the lower part of the shell. Three prominent 

 folds are present, on the inner side of the shell, formed by the intending of lx>th 

 layers of shell, and corresponding to the external grooves (A, B, C). Of these the 



