BIVALVIA. 139 
removed. In the clayey beds of the Hocene deposits the two valves are in contact, 
but the margins all round are so closely united that I am unable to see anything like an 
osselet. 
1. VerticorpIA rorMmosa, S. Wood. Tab. XXI, fig. 6 a, 4. 
Spec. Char. V. Testd minima, suborbiculari, vel spheroided, tumidd, inflata, tenut, 
inequilaterah, costaté; costis paucis, distantibus, intermediis, striatis; umbonihus 
prominentibus ; lunuld parvd, profundd ; apice acutd, valde incurvatd; marginibus 
crenulatis. 
Shell small, very tumid, thin, inequilateral, with a few large radiating riblets, and 
wide interspaces covered with striz; beaks small, incurved, rather prominent; lunule 
small, deep; margins crenulated. 
Diameter, + of an inch. 
Locality. Wondon Clay, Whetstone (Wetherell). 
A single specimen, unfortunately not in good condition, is in the cabinet of 
Mr. Wetherell, and as this came from a well-digging it may be some time ere another 
presents itself. Iam glad to have the opportunity of bringing it into notice, which the 
owner has kindly permitted me to do. Although not perfect, there is a small portion of the 
exterior of the shell remaining, and from this I imagine it did not possess more than half 
the number of riblets that there are upon sz/cata, perhaps not more than a dozen; these 
are not large nor very much elevated; they stand far apart, with a broad intervening space, 
and in this there are about three or four intermediate smaller rays or coarse strie. It has 
some slight resemblance to Z'rigonulina ornata (D’Orbigny). 
2. VerTicoRDIA oBLIeuATA, Ldwards, MS. ‘ab. XXLJ, fig. 8, a, 6. 
Spec. Char. V. Testa minima suborbiculari, tumidd, inflata, tenui, frayili; valde 
wnequilaterali ; costatd vel striolatd, costulis cirea 26, conveaxiusculis ; umbonibus promi- 
nulis, incurvatis, acutis ; lunuld parvd, profundd ; marginibus crenulatis. 
Shell minute, orbicular, tumid, and inflated, thin and fragile; very inequilateral ; 
riblets about 26, rounded; beaks incurved, sharp; umbonal region prominent ; lunule 
small, deep; margins crenulated. 
Diameter, 2ths of an inch. 
Locality. Bracklesham (Edwards). 
A single specimen of this species is all that I have seen. It appears to be distinct 
from the London Clay shell, differmg, as it does, in some particulars ; it is rather less in 
size, but this might be from difference in age. The ribs are not so numerous, and they 
