Figs. 
les 
A, 
PAR Xexe 
Triconta (continued). 
T. scapha, Agassiz. (P. 73.) 
1. Lower Greensand (probably Snettisham ironstone nodules), West Norfolk. The 
type of T. hunstantonensis, Seeley. Woodwardian Museum. Right valve. 
2. Snettisham Clay, one third of a mile south-west of Snettisham Church. Museum 
of Practical Geology. Portion of left valve. Drawn from a wax cast of an 
external mould. 
Genus—Myoconcua, Sowerby. 
M. cretacea, VOrb. Chloritic Marl, Maiden Bradley. Woodwardian Museum. 
a, right valve ; b, ornamentation of same xX 3. (P. 114.) 
Genus—Sponvyits, Linnzus. 
S. Roemeri, Desh. Perna-bed, Atherfield. Woodwardian Museum. a, left 
valve (umbo slightly restored); b, outline from the posterior end; ¢, right 
valve ; d, ornamentation of left valve x 3. (P. 116.) 
5—11. S.gibbosus, ’Orb. Cambridge Greensand (derived from the Upper Gault), 
Cambridge. Woodwardian Museum. (P. 117.) 
5, 6a. Left valves; 65, anterior outline; 6c, ornament of left valve x 2. 
7a. Left valve; b, posterior of both valves ; ¢, right valve. 
8a. Left valve; 6, part of same x 2. 
9a. Left valve; b, anterior outline. 
10. Left valve. 
11. Posterior outline of a specimen with talon-like right valve. 
