444» MANUAL OF THE MOLLUSCA. 
small, very deep, bounded by the second duplicature (m); thire 
dupheature (n) projecting into the umbonal cavity: free valve 
Fig. 933 tunterior of lower valve, 3. Fiz. 234. Upper valve (restored). 
Hippurites radiosus,Vesm. _ Lower chalk, St. Mamest, Dordogne.* 
a, a, adductor impressions and processes; c, c, cartilage pits; t,t’, teeth and dental 
sockets; uw, umbonal cavity; p, orifices of canals; 2, ligamental inflection; m mus- 
cular, 2 siphonal inflection. 
depressed. with a central umbo, and two grooves or pits cor- 
SASS nly, 
WEN | 
NS 
Fiz 255. Ai. Toucasionus, upper valve, 3.t Fig. 236. Lower valve, with mould, 2 
1 ligameatal, m mus ular, m siphonal infections; z, fracture, showing canals; 
e cartiagce: u, left nmboe; the arrows indicate the probable direction of the branchial 
cmrrents, 
e 
responding to the posterior ridges in the lower valve; surface 
* From the original in the Brit. Mus. The inner layer of shell in this species has an 
irxegniarly ceilular structure, to which its preservation is due. 
¢ 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 origx 
nals in Brit, Mus, 
oes a 
ntl 
x 
