48 A NATURALIST ON THE " CHALLENGER." 



rounded cavities in the rock excavated by the urchins for them- 

 selves, both in the calcareous sand rock and volcanic conglome- 

 rate. With these was a coral (Porites) which forms small rounded 

 masses, bright yellow or whitish pink in colour, and a grey Paly- 

 thoa, a compound sea anemone, that is a colony composed of 

 sea anemones closely joined together, and here forming sheet- 

 like masses often a foot in diameter, encrusting the rock. An 

 Aplysia, or sea slug, with a pair of large skin folds continued up 

 from the sides of the body, and lapping together over the back 

 of the animal, was common, and is probably the one referred to 

 by Darwin, as seen at St. Jago.* 



A Rock-crab (Grapsus strigosus cf.), was very abundant, run- 

 ning about all over the rocks, and making off into clefts on one's 

 approach. I was astonished at the keen and long sight of this crab. 

 I noticed some make off' at full pace to their hiding places at the 

 instant that my head showed above a rock fifty yards distant. 

 The crab often makes for the under side of a ledge of rock when 

 escaping from danger, and may then be caught resting in fancied 

 security by the hand brought suddenly over it from above. The 

 dry rocks were covered with the dung of the crab, which is in 

 the form of small brittle white sticks about an inch in length, 

 very puzzling objects at first sight. The cast shells of the crab, 

 which are bright red and very conspicuous, were lying all over 



the rocks. 



At Still Bay, on the sandy beach on which, although it is on 

 the leeward side of the island and the sea surface was smooth, 

 a heavy rolling surf was breaking, I encountered a Sand-crab 

 (Ocypoda ippeus), which was walking about, and got between it and 

 its hole in the dry sand above the beach. The crab was a large 

 one, at least three inches in breadth of its carapace. In this 

 species of crab, the eyestalks are very long. The eyes are on the 

 side of the stalks which are longer than eyes, and projecting 

 above them are terminated by a tuft of hairs. When the 

 animal is on the alert, these long eyestalks are erected and 

 stand up vertically side by side far above the level of the 

 animal's back. 



With its curious long column-like eyes erect the crab bolted 



* Darwin, " Journal of Researches," p. G. 



