From the ANNALS AND Maaazine oF Naturat History, 
Ser. 7, Vol. iii., June 1899. 
7 
Note on the Occurrence of Cytheridea castanea, G. S. Brady, 
ina Surface-deposit in the Vicinity of Buenos Ayres, South 
America. By Tuomas Scort, F.L.S. 
[Plate XVI] 
DarwWIn, when describing the surface-geology of the Pampas 
in his ‘Geological Observations on South America,’ alludes 
to the occurrence of shell-bearing sand-dunes on the shores of 
the Rio de la Plata and elsewhere in the province of La Plata. 
Numbers of these dunes are to be found in the vicinity of 
Buenos Ayres, especially towards the shores of the estuary of 
the Plate. The dunes referred to are generally more or less 
covered with vegetation, but in some instances, where the 
vegetation is displaced, a shell-bed a few inches thick and of 
a darker colour and firmer consistency than the sand is seen 
to stretch across each of the dunes in a nearly horizontal 
position. It is in this shell-bed that the Cythertdea was 
obtained that forms the subject of this note. 
Buenos Ayres, being an important seaport, is frequently 
visited by ships trading to South America. My younger son, 
Mr. John Scott, is a marine engineer, and his ship happened 
to be at Buenos Ayres for several days during January last? 
year (1898). My son is interested in natural history, and, 
being ashore, he took the opportunity to examine a few of 
the sand-dunes in the vicinity of the harbour of Buenos Ayres 
and also to collect a quantity of the material in which the 
shells are embedded. In collecting this material he first 
scraped away the surface-matter, then, digging well into the 
shell-bed, removed what he considered to be a fair sample of 
the material ; this he brought home on his return to England. 
I made a careful examination of the material my son had 
brought to me, and obtained from it a number of different 
kinds of fossils ; the most common species obtained was Azura 
labiata, d’Orb., a bivalve mollusk mentioned by Darwin as 
