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NOTE ON THE SHELLS OF SCHIZODESMA SPENGLEBI LINN. 
By J. D. F. Gilchrist, M.A., D.Sc, Ph.D. 
The sands of Muizenberg, though at tmies so apparently barren and 
devoid of animal life, prove on closer acquaintance to present many features 
of interest for zoological study. Frequently after a strong " south-easter " 
there are cast up many diverse forms of pelagic life. Millions of Physalias, 
the "Portugese Man of War " or " Blue Bottle " as they are called locally, 
may form a blue band at high-water mark extending for miles along the 
shore. Among them are other pelagic forms — Porinta, Velella, lanfhina, 
etc. Over the wet sand may be seen hurrying about the little active mollusc, 
Bullia digitalis, and under it are multitudes of "White Mussel,'" Bonax 
serra, and many burrowing prawns, whose presence is only indicated by the 
openings of their burrows at the surface. After a north-west wind other 
forms appear, brought up by the under-current, such as masses of " red 
bait " and various kinds of shells, prominent amongst which is a large 
bivalve (Schizodesum sj^engleri). 
It is, however, not only the zone between the tide-marks that is of 
interest, but also the zone above high-water mark, for here the fine sand has 
been carried back by the wind to form the long line of high sand-dunes, and 
the heavier shells have been left exposed in profusion. 
It is to a peculiarity amongst these that I wish to direct attention. They 
consist of a variety of different kinds and from various sources. The 
delicate blue shells of the pelagic lanthina are sometimes found intact, as 
well as the thin shell of the "toe loeppel," or " teaspoon shell " (Lima Mans). 
The stouter shells of other bivalves, such as Venus verrucosa, Dossinia, 
ecoleta, Donax serra, Lutraria ohlonga and Macfra glahrata are to be found 
in abundance, but the commonest is the large bivalve Scliizodesma sjjengleri, 
readily recognised by its large thick valves, with a strong ridge along its 
outer surface. It is known to fishermen as the " Doed-Mossel." It is a 
sub-genus of Mactra and is peculiar to the Cape of Good Hope. 
This shell is the largest and one of the stoutest of the shells, and yet, as 
may be readily noted, it is the one of which most broken fragments are to be 
seen. Moreover, these fragments are not like those of other shells as a rule, 
for the fracture appears to be sharper and unweatliered. Again, it may be 
