358 SYNOPTIC COLLECTION. 



ance to the otherwise circular outline, as already pointed 

 out. 



The carapace sometimes becomes ornamented with 

 spines, as seen in Pericera cornuta M. Edw. (No. 877). 

 Two long divergent spines extend forward, while the next 

 longer pair protect the closed tubes for the eye-stalks. 

 The walking-legs (not seen in the specimen) are free 

 from spines. 1 



The spider crab, Metoporhapis calcarata Stimp. (No. 

 878), resembles a spider in having a small cephalothorax 

 and extremely long legs. The former appears to have 

 been pushed upward in front, so that the slender, sharp 

 rostrum, instead of extending forward as in most Crus- 

 tacea, points almost vertically upward. The posterior 

 part of the cephalothorax also appears to have been 

 crowded upward and forward with the result of bringing 

 the last or fourth pair of kgs very nearly over the third 

 pair. In the process the carapace has been shortened, 

 so that the last segment of the thorax is exposed. The 

 arms with their claws are slender and extend forward. 

 The rostrum and the large spikes of the legs are tipped 

 with two tiny spines. 



A relative of the spider crab is Dorippe lanata Bosc. 

 (No. 879). In this case the hind pair of walking-legs 

 are pushed up on the back and being of no use for loco- 

 motion in this position they have become vestigial. The 

 third pair of legs are undergoing the same process, being 

 much smaller and shorter than the first and second pairs. 

 The latter are long and spider-like. The claws are little 

 organs and their position indicates that they offer efficient 

 aid to the mouth parts. 



One species of Dorippe (D. facchino} is of especial 

 interest, since it is never found without a sea-anemone 

 (Cancrisocia expansa St.) on its back. This is an admir- 

 able illustration of commensalism, since neither animal 

 is ever found excepting in each other's company. 



1 Miers, Journ. Linn. Soc. London, XIV, 1879, p. 664. 



