HABITS OF THE FOUR-HORNED SPIDER-CRAB. 249 



the Museum aquaria by the Four-horned Spider-Crab are green 

 and brown seaweeds of various kinds, and Sertularia operculata, 

 and Bugula turbinata. Other individuals have borne Hali- 

 chondria panicea, Spirorbis, and (in two cases) the golden-yellow 

 Botryllus gemmeus ; but these foreign bodies were already on the 

 Spider-Crabs when they were obtained from the sea. Aurivillius* 

 records the use of hydroids and algae, and Garrington and 

 Lovett f the use of Plumularia falcata, I Alcyonium digitatum, 

 and Halichondria panicea. Schmidtlein § mentions the use of 

 sponges, Alcyonium, Sertularia, Antenntdaria, Flustra papyracea, 

 and colonies of synascidians in " Pisa-species," but does not 

 specifically mention P. tetraodon. One of the individuals 

 observed by me which bore a mass of Botryllus gemmeus also 

 carried a white plume of dead Bugula turbinata, of about an 

 inch and a half in length, on its carapace ; and it may 

 be remarked that the golden-yellow Botryllus and the white 

 Bugula were so conspicuous that the brown Spider- Crab itself 

 was easily overlooked. The plume of Bugula fell off, or was 

 knocked off* the back of the Spider-Crab during the night, and, 

 after lying for a couple of days on the floor of the tank, was 

 replaced by the Spider-Crab. Although the Spider-Crabs will 

 place disguising materials upon their bodies during the daytime, 

 it is after dark that they prefer to work, and it is then they work 

 most quickly. Two females which lived together in an aquarium 

 were given three masses of Sertularia operculata, each of about 

 the size of an open hand, at 10 a.m. They examined the Sertu- 

 laria, and seated themselves in the midst of it, but they made 

 only few, and but partly successful, attempts to fasten it amongst 

 their hook-like hairs in the daytime. On the following morning, 

 however, it was found that both were completely enveloped in 

 masses of the hydroid, which they had fastened to their bodies. 

 The small hook-like hairs upon the carapace and backs of 

 the legs to which the disguising materials are attached have 

 often been described in the different species of Spider-Crabs. It 

 should, however, be observed that the seaweeds and hydroids 



* Op. cit. p. 49. f Loc. cit. p. 359. \ = Hydrallmania falcata. 



§ R. Schmidtlein, " Beobachtungen Tiber die Lebensweise einiger 

 Seethiere innerhalb der Aquarien der Zoologischen Station," ' Mittheilungen 

 aus der Zoologischen Station zu Neapel,' Erster Band, 1879, p. 23. 



