448 ZOOLOGY OF THE FAR EAST. 
remaining specimens from this locality had the pleon segments similarly armed with 
spinules but occasionally the pair on the second pleon segment and one of the pairs 
on the third pleon segment were absent. The setae on the uropods were only found 
on adult males. In other characters the specimens were in substantial agreement 
with the specimens from L. Biwa. All had accessory branchial vesicles on the bran- 
chial lamellae. 
The specimens from St. 13 are quite small and immature. The pleon segments 
have the following arrangements of spinules commencing with somite : i, o prs, 2 prs, 
4prs, 3 prs, 3 prs, 2 prs. There are thus many more spinules on the pleon than in the 
typical form. Moreover, there is a greater development of setae on the antennules 
and antennae. But both these characters appear to become less pronounced with 
age. The setae on the antennules and antennae become fewer and the spinules on 
the pleon reduced in number. 
The specimens from Komatsu, from the interior of Spongilla dementis, are also 
young specimens. The number of pairs of spinules on the pleon segments is o, i, i, 
2, 2, I. These specimens are therefore less spinulose than those from St. 13, but in 
having spinules on the second and third segments of the pleon they show a divergence 
from type. 
The specimens obtained in 30 feet of water off Komatsu are seven in number and 
include a typical male of G annandalei, ri mm. in length and agreeing with the type 
in the spinulation of the pleon. The smaller specimens from 4-8 mm. in length have 
more spinules cn the pleon and in four of them there are spinules on the second and 
third segments. 
It will be seen therefore that there is considerable variation in the specimens in 
two characters : — 
(1) The number and arrangements of spinules on the segments of the pleon. 
(2) The development of setae on the antennules, antennae, telson and uropods. 
This variation is of two kinds : — 
{a) Variation with age. In the L. Biwa specimens there is definite evidence that 
young specimens have more spinules on the segments of the pleon and a greater 
development of setae on the antennae and antennules. 
[h) Variation of specimens of approximately equal age from different localities. 
The Sapporo specimens have a greater number of spinules on the segments of the 
pleon, more setae on the telson and, in adult males, a development of setae on the 
inner margin of the outer branch of the third uropods. 
But similar types and degrees of variation are known in Gammarus pulex and 
there seems no reason to regard it as of specific importance in the present cases. 
In his synopsis of the Amphipoda Gammaridea, Stebbing (1906) gives a key to 
thirty species of the genus Gammarus and an additional species {G. tunitanus, Simon) 
is regarded as doubtful. In the appendix to this valuable work a further seven 
species of the genus are listed, and, since its publication, as far as I can make out, six- 
teen new species have been referred to the genus which now comprises fifty-four 
species. 
