74 A HISTORY OF RECENT CRUSTACEA 
down and clear away any clinging particles of sand. Mr. 
David Robertson had a female of this species alive in his 
possession for seven months, and, so far as his observation 
went, it would le buried for weeks without seeking to 
change, the antenne clasping into each other to form the 
tube necessary for its breathing, by giving access to the 
water above. Through this tube he was also fortunate 
enough to see the ova sent up, and he infers that the 
animal at the proper time places them within the influence 
of the current which its breathing apparatus must con- 
stantly maintain. He notices that the pleon by its small 
size is less fitted to cover the ova than is generally the 
case among the Brachyura, but that this is compensated 
and accounted for by the burrowing habit. 
In a very young specimen, scarcely three tenths of an 
inch long, the ‘front’ quite differs from what is seen in 
the adult, being produced into a conspicuous rostrum as in 
the genus Galathea, and the telson, instead of being 
rounded, is broadly emarginate. As two genera, Nautilo- 
corystes and Pseudocorystes, were so named by Milne- 
Edwards in 1857, to indicate their great resemblance to 
the earlier genus Corystes, it may be interesting to point 
out some of the differences by which the three are dis- 
tinguished, and which in the early days of classification 
would probably have passed unnoticed. 
Corystes.—The third maxillipeds have the fourth joint 
longer than the third, with the fifth joint inserted 
in a deep notch of its inner margin considerably 
below the apex. In the fifth pair of legs the 
seventh joint is narrow. 
Nautilocorystes.—The third maxiliipeds have the fourth 
joint a little shorter than the third, with the fifth 
joint attached at its apex. In the fifth pair of 
legs the seventh joint is widened. 
Pseudocorystes.—The third maxillipeds have the fourth 
joint much shorter than the third, small, triangu- 
lar, with the fifth joint attached near the apex. 
In the fifth pair of legs the seventh joint is 
widened. 3 
