i44 



MANUAL OF THE MOLLUSCA. 



small, very deep, bounded by the second duplicature {m) ; tbird 

 duplicature (?i) projecting into the umbonal ca\^ty : free valve 



Fiff. ?33 interior o*^ lower valve, |. 



Fig. 234. Upper valve (restored). 



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

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

 sockets; u, umbonal cavity; jo, orifices of canals; I, ligamental inflection; »i mus- 

 cular, n siphonal inflection. 



depressed, with a central umbo, and two grooves or pits cor- 



Fig. 2b5. R. Tour.annnus. tipper valve, |.t Fig. 236. Lower valve, with mould, | 

 I ligameatal, m nus , alar, n siphonal inflections ; x, fracture, showing canals ; 



c cani'ase ; m, left ruxbo ; the arrows indicate the probable direction of the branchial 



cQireurs. 



responding to the posterior ridges in the lower valve ; surface 



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

 liKO^uiaily cellular structure, to which its preservation is due. 



t lliis internal mould, representing the form of tne anioaal, was obtained by remov- 

 ioj, die upper valve piecemeal with the chisel ; a plaster-cast taken from it representa 

 tue interior of tha upper vaive, witu the base^ oi the teeth and apophyses. See orife> 

 nals in Brit. Kuji. 



