167 



Guppy Reprint J 9 



Page 39 



beach. We must - look, therefore, for a condition inter- 

 mediate between the two as probably 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 

 Litorincz, Patella, and Ncrita. None of these 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 

 turgida, M. carinata, Trigona mactroides, Dojiax denticu- 

 lata, D. striata, and more rarely Ve?ius granulata, Cy- 

 therea 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, 

 Ccrcum, Dentalium, &c. , &c, and several of the Conchi- 

 fera. The only strictly litoral gasteropod in this col- 

 lection, viz., Chiton, is represented by a solitary plate. 

 As to the two freshwater species, each of which is 

 represented by a single example, the} 7 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 fossil 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 common 

 during the deposition 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 pygm&a is not quite so 

 numerously 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. 



