4 
ORBICULA reflexa. 
TAB. mi.— Jig. 1. 
Spec. Char. Shell subelliptical,, most pointed to- 
wards the back, polished ; upper valve rather 
convex, with the vertex near the posterior mar- 
gin ; lower valve flat with a nearly central ver- 
tex, the margin reflected ; sinus for the byssus 
large, elongated. 
Syn. Orbicula reflexa. G. B. Soiverby , Zoological 
Journal , v. 2. p. 321. 
Although a great part of the lower valve is flat, yet 
the portion behind the focus or apex is concave, be- 
ing gradually bent inwards towards the sinus, which ex- 
tends from the focus to the margin, and terminates 
where that begins to be reflected. The upper valve co- 
vers the reflected edge of the lower, in the same way 
that the upper valve covers or incloses the other in the 
genus Produeta, Both valves are smooth and very thin ; 
and, the lower especially, beautifully marked with con- 
centric lines and zones of a light colour : they seem to 
have contained a large portion of animal matter, and are 
very fragile, easily dividing into very thin, translucent 
laminae. We cannot discover any traces of impressions 
of muscles or ligaments, yet we do not doubt the pro- 
priety of placing this species in the same genus with the 
recent ones. 
A number of these curious shells were found in one 
or two broken Clay Ironstone nodules, buried, — with 
