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beach. We must look, therefore, for a condition inter- 
mediate between the two as probabh" the nearest to the 
truth. And we find that the fauna is one which would 
suit a depth of from twenty to fifty fathoms. On those 
tropical beaches where univalves predominate, we have 
Litorinee, Patella, and Nerita. None of the.se are re- 
presented in the Matura beds. On the other hand, on 
those long stretches of seabeach in the tropics where 
the molluscan fauna is chiefly bivalve, we find Mactra 
tiirgida, M. carmata, Trigona mactroides, Donax de?itic7i- 
lata, D. striata, and more rarely Venus granulata, Cy- 
thcrea dione, and a few Tellens. In the deposits at 
Matura we have, however, shells characteristic of a 
certain depth of water : such as Terebra, Oliva, Mar- 
ginella. Conus, Erato, Chemniztia, Eulima, Odostomia, 
Ccecum, Dentalium, &c., &c., and several of the Covchi- 
fcra. The only strictly litoral gasteropod in this col- 
lection, viz.. Chiton, is repre.sented by a solitary plate. 
As fo the two freshwater species, each of which is 
represented by a single example, the}' may have been 
borne out on floating wood or otherwise, from some 
stream of the neighhouring land. 
The comparative numbers of the individuals of each 
species found in the fo.ssil and recent condition is an- 
other matter which deserves some consideration, though 
I fear I cannot make many observations of a complete 
and accurate nature on that head. The little rice snell, 
Oliva oryza. seems to have been almost as conunou 
during the depo.sition of the Matura beds as at pre- 
sent : while the Astarte {Gouldia martinicensis) is much 
more rare now than it would appear to have been for- 
merly. This small shell occurs in immense numbers 
in the Matura deposit. Corbula pygmcea is not quite so 
numerou.sly represented. The latter is by no means 
rare in some localities at the present day, but it is 
.second only to the Astarte before mentioned in point 
of numbers in the Matura deposits. 
