TANAIS, 128 
The tail in this genus consists of less than the normal 
number of segments, and carries only three pairs of 
pleopoda and a pair of terminal uropoda. The segments 
may vary in development and distinctness, being more or 
less fused together, in the different species. In one 
or more species (constituting the genus Crossurus of 
Rathke) two of the segments are furnished on the 
upper surface with transverse fascicles of long hairs, 
and on the under-side with two pairs of delicate oval 
membranous plates, strongly ciliated, supposed by 
Edwards to constitute the breathing apparatus, but into 
which F. Miller affirms not a single blood corpuscle 
ever enters. Hach pair of these plates is fixed upon 
a common base, and is laid transversely when at rest, 
thus differing from the general arrangement of these 
organs. 
The terminal segment of the body is furnished at 
the sides with a pair of short, slender, articulated, fila- 
mentary appendages, consisting, in 7. Savignyi and T. 
Edwardsu, of a strong basal joint followed by a six or 
seven jointed flagellum, at the base of which is affixed 
a minute oval appendage setigerous at its tip. In the 
species which we have figured this appendage consists 
of only three or four distinct joints. 
As yet we are but imperfectly acquainted with the cha- 
racteristics of the species as well as with the distinction 
of the sexes, habits, &c. The typical species (Gammarus 
Dulongii, Andouin) was from Egypt, and is beautifully 
illustrated by Savigny in the great work on that country. 
In Kro6yer’s monograph of the genus, published in the 
fourth volume of the “ Naturhistorisk Tidsskrift,” seven 
species are described, namely, 7. Edwardsii and Savignyi 
from Madeira, 7. dubius from Bahia, in Brazil, T. gracilis 
from Spitzbergen, J. tomentosus from the Norwegian 
Sea, and 7. Orstedii and T. Curculio from Oresund. The 
