ii 
TRIG ONI A eccentrica. 
TAB. CCVI1L — Figs, l and 2. 
Syn. Trig-oni a eccentrica. Parkinson , vol. iii. 
p. 175. tab. 12. f. 5. 
Spec. Char. Transversely ovate, convex; ante- 
rior side produced, posterior side round, with 
oblique undulating ridges on the surface. 
The length is only half the width ; the edge is very re- 
gularly curved till it comes to the produced part of the 
anterior side, where it bends a little forward, and then 
turns suddenly back. The ridges are straight and trans- 
verse near the beaks where they almost cross the shell ; 
those placed nearer the front are confined to the posterior 
side, are undulated, and are crossed by the lines of 
growth. 
1 have given two views of one valve, which was found 
on Black Down by the Rev. J, H. Steinhauer; it is 
silex, stained perhaps by vegetable matter. I have the 
opposite valve imperfect from Hembury Fort, Devon- 
shire, through the hands of Mr. Goodhall : also silicious. 
TRIGONA affinis. 
TAB. CCVITI. — Fig. 3. 
Syn. Trigona affinis. Miller , MSS. 
Spec. Char. Transverse, oval, gibbose, half 
covered by transverse ridges. 
V ery thick, regularly elliptical, about one-third wider 
than long, and remarkable for the slight protuberance of 
the beak, behind which there is not that cavity observable 
in Corbula, and many other shells. The transverse 
