444 



MAKTTAL OF THE MOLLtJSCA. 



small, very deep, boimded by tlie second duplicature (m) ; tMi-d 

 duplicature {n) projecting into tlie iinibonal cavity : free valve 



Fig. 233. Interior of lower valve, |. 



Fig, 234. Upper valve (restored). 



Hippurites radiosus, Desm. Lower chalk, St. Mamest, Dordogne.* 

 a, a, adductor impressions and processes ; c, c, cartUage pits ; t, t', teeth and dental 

 sockets; m, umbonal cavity; p, orifices of canals; I, Ugamental inflection; m mus- 

 cular, n siphon al inflection. 



depressed, witli a central umbo, and two grooves or pits cor^ 



Fig. 235. B. Toucasianus, upper valve, |,t Fig. 236. Lower valve, vpitii mould, | 

 I Ugamental, m muscular, n siphonal inflections; x, fracture, showing canals) 



c, cartilage ; u, left umbo ; the arrows indicate the probable direction of the branchial 



cturents. 



responding to the posterior ridges in tlie lower valve ; surface 



* From the original in the Brit. Mus. The inner layer of shell in this species has an 

 irregularly cellular structure, to which its preservation is due. 



t This internal mould, representing the form of the animal, was obtained by remov- 

 ing the upper valve piecemeal with the chisel ; a plaster-cast taken from it represents 

 the interior of the upper valve, with the bases of the teeth and apophyses. See origi- 

 nals in Brit. Mus. 



