4i6 
ZOOLOGY OF THE I'AR EAST. 
A. hilgendorfii, Bovallius. 1886, p. 13. 
A. hilgendorfii, Hilgendorf, 1893, p. i. 
Locality: — Stations 5,6,8,10,14 and 22, Lake Biwa, Japan, abundant, length up 
to 10 mm. 
It was a matter of great interest to discover this cosmopohtan species in the 
collections from Japan. After careful examination, I can find no vital points of 
difference between these specimens and those I have examined from this country. 
The Japanese form is perhaps somewhat smaller and slightly narrower and there are 
fewer setae on the second pleopod of the male, but these differences are very slight. 
In 1874, Hilgendorf recorded a species of Asellus from Japan in the following 
words " In Graben der Stadt Yedo ist von mir eine Siisswasser-Assel aufgefunden 
worden. Die fragliche Aselliis-Artis von der Europaeischen (dem A. aqiiaticus) in 
mehrfacher Beziehung verschieden : der Lieb ist schmaler, das vierte Beinpaar stark 
verkurzt und am letzten Segment iste die Spitze einfach gerundet (in der Mitte 
nicht eingekerbt). Ein Vergleich mit den Nordamerikanischen Arten ist mir nicht 
moglich." 
On the strength of this, Bovallius in 1886 named the species found by Hilgen- 
dorf as A . hilgendorfii without having seen specimens and merely quoting the above 
passage from Hilgendorf as a diagnosis of the species. 
In 1893, Hilgendorf published a few notes on this species. He says that his 
previously published remarks were written after a comparison of. his Japanese 
specimens with the description and figures given by Bate and Westwood. 
On comparing his Japanese specimens with actual specimens of .4. aquaticus 
from Europe he found that the differences in the shape of the posterior end of the 
metasome and in the comparative lengths of the fourth and fifth thoracic limbs, 
which he had noted as characterising the Japanese form, did not in reality exist. 
He does note, however, that in .4. aquaticus from Europe the fifth thoracic limbs are 
only 1/8 shorter than the fourth, while in the Japanese specimens, the fifth thoracic 
limbs are from 1/4-1/3 shorter than the fourth. He notes as further differences that 
(i) A. hilgendorfii is a more slender form than A. aquaticus, 3 1/3 times longer than 
broad as against 2 1/2 times in A. aquaticus, (2) the second antenna is only 3/5 of the 
total length of the body as against 4/5 in the European form and (3) that the 
uropods in .4. hilgendorfii have a shorter and broader basal joint and shorter 
branches. He goes on to remark that in the number of ocelli of the eyes, and, what 
is of great importance, in the form of the pleopods of the male, the Japanese species 
agrees absolutely with the European one. 
With regard to the differences named by Hilgendorf I find (i) the European 
species is about three times as long as broad, certainly over 2 3/4, (2) that there is no 
appreciable difference in the length of the antenna in Japanese and European speci- 
mens, (3) that the character of the uropods is not a safe one to rely on, as these 
appendages are constantly found in a regenerated form after having been broken off, 
(4) that the difference in the length of the fourth and fifth thoracic limbs in two 
measured specimens, one of a Japanese specimen and the other of a British are as 
