214 FRESH-WATER NEREIDS FROM THE PACIFIC COAST AND HAWAII. 



from Hawaii and from Lower California there is considerable thickening of the epi- 

 dermis in places, particularly on the sides in Lycastis hawaiiensis (PL XVII, Fig. 22). 

 Making due allowance for the smaller size of the species it is about as thick in the 

 same regions in Lycastoides alticola. 



V. CONCERNING LYCASTIS. 



The recently published memoir by Gravier (:01 a ) on this genus might be thought 

 sufficient for the present, particularly as I have so little that is new to add; but unfor- 

 tunately Gravier's paper is not accessible to all who may be interested in this remark- 

 able section of the Nereidse. Hence this brief account is offered. 



The genus Lycastis was founded by Savigny ('20) for the reception of Nereis 

 armillaris 0. F. Muller, which, however, proved to belong to the genus Syllis. The 

 name was afterwards adopted by Audouin et Milne-Edwards ('32-'34, p. 199) for a 

 new nereid, Lycastis brevicornis, which they had discovered on the west coast of 

 France. The type-specimen remains unique; no one, apparently, has rediscovered 

 the species. Seven species have since been added, all but one of them tropical. The 

 known species are : 



L. brevicornis Aud. et M.-Edw. ('32-'34), W. coast of France. 



L. quadraticeps Gay ('49), Chile. 



L. abiuma Grube ('72), Desterro, Brazil. 



L. littoralis " 



L. senegalensis St. Joseph (:01), Senegal R., W. Africa. 



L. ouanaryensis Gravier (:01), French Guiana. 



L. geayi 



L. hawaiiensis sp. nov., Hawaii. 



It is seen that the "metropolis" of the genus is the east coast of South America, 

 within the tropics, where half the known species belong. Two other tropical species 

 have been described, and only two extra-tropical ones. The genus, therefore, is 

 principally one of the tropics. 



The foot of Lycastis is remarkable among the Nereidse for invariably lacking, 

 almost if not quite, the whole of the dorsal ramus. In all species the dorsal cirrus 

 remains. It is often much enlarged, becomes highly vascular, and is flattened to 

 form a leaf-like structure which functions as a gill. L. quadraticeps and L. littor- 

 alis are exceptional, for in both the dorsal cirrus is small. It should, however, not be 



