120 TANAIS. 



cylindrical joints and a rudimentary flagellum, svhich is, 

 however, considerably elongated in some species, as in 

 T. Edwardsii, where it is seven-jointed; according, how- 

 ever, to Fritz Muller, the sexes differ in the structure 

 of their antennae. A small auditory cavity exists in 

 the first joint of the peduncle. These antennas are 

 attenuated to the tip, which is furnished with a strong 

 pencil of hairs. The lower antennas resemble the upper 

 in direction and length, but they are more slender, and 

 consist of a five-jointed peduncle, of which the first 

 and third are short and ring-like, and the fifth is also 

 terminated by a few hairs, within which is also a rudi- 

 mentary flagellum. The mouth is well formed for biting. 

 The upper lip is conical, resembling that of the Gammari, 

 with a ridge along the medium line terminating in a 

 produced point. The lower lip is formed of two ovate 

 pieces fixed obliquely, united together at their extremity, 

 leaving a triangular space between them, arising from 

 a reversed triangular piece rounded at its base.* The 

 mandibles are horny and elongate-triangular, terminated 

 in a denticulated point rather incurved, with a deep 

 impression and a movable denticulated tooth fixed be- 

 neath the apex ; towards the base on the inner edge, is 

 a strong somewhat squared molar tooth, truncated, and 

 having the entire edge of the truncated part notched 

 for chewing : in the middle of the outer edge is a small 

 tubercle emitting a short bristle, probably representing 

 the mandibular palpus. The inner pair of maxillas 

 are strong, formed of a long, curved, sub-cylindrical 

 outer portion, with the apex truncate and spinose, and 

 a biarticulated inner division with the tip of the second 



* We believe this piece, represented by Savigny as described above (and 

 more nearly agreeing with, the figure of the same organ in Gammarus than in 

 Cymofkoa), is identical with the piece described under the name of Under- 

 Iceben by Kroyer (Tidssk. iv. 170). 



