TANAIS. 123 



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. Miiller affirms not a single blood corpuscle 

 ever enters. Each 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 T. Savignyi and T. 

 Edwardsii, 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 Kroyer's monograph of the genus, published in the 

 fourth volume of the " Naturhistorisk Tidsskrift," seven 

 species are described, namely, T. Edwardsii and Savignyi 

 from Madeira, T. dubius from Bahia, in Brazil, T. gradlis 

 from Spitzbergen, T. tomentosus from the Norwegian 

 Sea, and T. Orstedii and T. Curculio from Oresund. The 



