1899.] A. Alcock — New and Rare Species of Crustacea. Ill 



Natural History Notes from the Royal Indian Marine Survey Ship 

 * Investigator,* Commander T. H. Ileming, B. JV., commanding. — 

 Series III. No. 3. On some Notable New and Rare Species of 

 Crustacea. By A. Alcock, M.B., C.M.Z.S., Superintendent of the 

 Indian Museum. 



(Plate I.) 

 [Received July 28th ; Read August 2nd, 1899.] 

 Contents : — 

 § 1. On a new Hermit-crab exhibiting perfect commensalism with a Sea-ane- 

 mone. 

 § 2. On a new species of Crab of the genus Domecia. 



§ 3. On a new species of Latreillia, and on the occurrence of Latreillopsis in 

 the Andaman Sea. 



Among the collections recently sent to the Indian Museum by Cap- 

 tain A. R. Anderson, I. M. S., lately Surgeon-Naturalist to the Marine 

 Survey, are a large number of specimens of a new form of Plermit- 

 crab, a single specimen of a new species of the curious little Coral- 

 crab Domecia, a new species of Latreillia, and specimens of Latreil- 

 lopsis hispinosa. 



§ I. On a new Hermit -a-ah exhibiting adaptive commensalism with a 

 Sea-anemone, 



The Hermit-crab is noteworthy (1) in having for its refuge, not 

 the usual mollusk- shell, but a sheet or blanket formed by the coenosarc 

 of a colony of Sea-anemones, (2) in being — as far as the male is con- 

 cerned — symmetrical, and (3) in having the appendages of the 3rd-5th 

 somites of the male and of the 2nd-5th segments of the female present 

 on the right or left side indifferently. 



Symmetry in Hermit-crabs is, of course, nothing new : Pomato- 

 cheles is perfectly symmetrical, as also are Ghiroplatsea and Pylocheles 

 (if these two genera are really distinct from Pomatocheles) : also sym- 

 metrical are Qlaucothoe, Mixtopagurus, Xylopagurus, the male of Gryllo- 

 'pagurus, some species of Gancellus, and lastly, though in a different 

 way, Ostraconotiis, Tylaspis, and Porcellanopagurus. 



[In our new form the male is symmetrical somewhat in the same 

 way as in the three genera last named ; that is to say, the abdomen is 

 a soft bag without any lateral twist.] 



Nor is there anything unusaal in the fact that the protective 

 covering of the abdomen is not a mollusk shell ; for in these seas alone 

 there are several well-known instances of Hermit-crabs making use 

 of other convenient receptacles. For instance, Pylocheles Miersi is 

 found impacted in hollow twigs of sunken drift wood ; Troglopagurus, 

 according to Messrs, Thurston and Henderson, lives in small cavities 



