414 Mr. H. A. Baylis on Two neio 



LI. — Two neiv Species of Monhystera (Nematodes) in- 

 habiting the Gill-chambers of Land-crabs *. By H. A. 

 Baylis, B.A. 



(Published by permission of the Trustees of the British Museum.) 



Dr. Charles B. Wilson, of Westfield, Mass., has kindly 

 submitted to me for examination some small worms which 

 were found by him in the gill-chambers of land-crabs in 

 Jamaica during July 1910. They prove to be minute 

 Nematodes belonging, apparently, to the free-living genus 

 Monhystera, Bastian. They are of two species, and came 

 from two species of crabs, determined by Dr. Wilson as 

 Oecarcinus ruricola and Cardisoma gnanhumi. Of these 

 species, the former provided examples of both Nematodes, 

 the latter only of one. 



The chief points of interest to be noted with regard to 

 these "parasites" (the word is here used in a broad sense) 

 are : (1) that they belong to a genus the species of which 

 are commonly found leading a free existence in the earth or 

 in fresh water, and are not known to have a parasitic phase ; 

 (2) that both the forms, as found in the crabs, appear to be 

 cither hermaphrodite or parthenogenetic, and at first sight 

 seem to be all females; and (3) that they are evidently not 

 specially adapted for a " parasitic " mode of life, inasmuch 

 as the number of young produced by one female is com- 

 paratively small, and these young are apparently hatched 

 from the egg before birth. 



In order to facilitate the description of the new species, 

 I shall employ certain formulae for expressing the relative 

 lengths of various parts of the body. For this purpose 

 I prefer the system of de Man f to that of Cobb J, as being; 

 simpler and requiring less mathematical calculation §. 



* Other notes on the fauna of the gill-chambers of the Geearcinidye 

 will be found in the following papers : — Wilson, C. B., " Crustacean 

 Farasites of West' Indian Fishes and Land Crabs," Proc. U.S. Nat. Mas. 

 vol. xliv. p. 189 (1913). Baylis, H. A., « Ohgochzeta " in Brit. 

 Antarctic ('Terra Nova') Exp., 1910, Zoology, vol. ii. no. 2, p. 13 

 ( Brit. M us.,' 1915) ; and " A Parasitic Oligochaste, &c," Ann. & Mag. Nat. 

 Hist. (8) xv. p. 378 (1915). 



t ' Die frei lebenden Nematoden der Niederlandischen Fauna,' T884. 



t "Arabian Nematodes," Proc. Linn. Soc. N.S.W. (2) v. 1890, p. 449. 



§ In adopting de Man's system, I follow the example of some other 

 writers on free-living Nematodes, e.g. H of manner and Menzel in various 

 recent memoirs on the group (Rev. Suisse Zool. xxiii. no. 5, 1915, and 

 other papers). 



