ISOPOD GENUS LIGIDIUM. 827 



unguis in all species but L. japonicum, in wliicli, according to 

 VerhoefF, the 7th foot has four ciliated bristles projecting beyond 

 the unguis. 



Pleopods. In the male the 1st and 2nd pairs are modified. 

 The 1st endopod is drawn out on the inside into a process upon 

 which is set a variable but small number of setre. The 1st 

 exo[>od has nlso setfo on tl\e postero-median corner. The 2nd 

 endopod is of two segments and greatly elongated. The inner 

 edge is thickened, and the outer appears to be folded over in some 

 forms. At the end of the distal segment this fold sometimes 

 becomes a wide lappet, which shows considerable individual 

 variation in size and shape. VerhoefF bases a key on the 

 characteristics of the male pleopods, but although my material is 

 not conclusive, I do not feel disposed to allow much iniportance 



Text-figure 2. 



JLiffidium hypnorum. a, antenna ; h, nntennule. 



to them. I suspect that they appear diflierent in forms collected 

 during and out of the breeding-season. (Text-figs. 3, e ; 4, a & 6 • 

 6,d,e&f; 8,c&,d; 10, c&d.) 



Uropods. The striking inequality of the two rami and the 

 characteristic inner process of the base make these appendages 

 systematically valuable, a fact Avhich causes their brittleness to 

 be all the more regrettable. Budde-Lund divides the species 

 dealt with by him into two groups — the first in which the exopoil 

 is longer than the endopod, and the second in which the reverse 

 is the case. Further knowledge has shown that the first group 

 contains but two species — the common L. hypnorum and Typhlo- 

 ligidkim caecum, — and that all the other known forms fall into 

 the second group. The grouping does not seem to be of primary 

 importance. (Text-figs. 4, c ; G,g; 8, e; 9, c; 10, e.) 



