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 lie buried for weeks without seeking to 

 change, the antennae 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 loDg, 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 1837, 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 maxillipeds 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. 



