1897.] 



NATURAL SCIENCES OF PHILADELPHIA. 



397 



tubercles ; the median line is also tubercular. The legs are long and 

 slender on the 7th segment, a little shorter on the 6th, and so on to 

 the 1st which are quite short. 



The abdomen is markedly narrower than the 7th segment, it tap- 

 ers gradually to a point near the end which is broad and well 

 rounded, the median line ends in a small concavity best seen with a 

 lens. Excepting the usual lateral incisions, the upper surface is 

 smooth and glabrous. 



A large male measures 22 mm. in length and 7.5 in breadth ; a 

 female, with eggs, 12 mm. in length and 4.5 in breadth. 



Not less than one thousand specimens of this species were dredged 

 off Chirikoff Island, Alaska, at Station 3,340, lat. N. 55° 26' 00", 

 Ion. W. 155° 26' 00", 695 fathoms (No. 20,500, U. S. N. M.). 



Synidotea erosa, new species. Fig. 8. 



Several specimens of this species 

 were dredged at Station 3,210 oft* San- 

 nakh Islands, Alaska, in 483 fathoms ; 

 lat. N. 54° 00' 00", Ion. W. 162° 40' 

 30" (No. 20,505, U. S. N. M.). 



Erosa is more nearly related to S. 

 pallida than to any species yet dis- 

 covered, as in the latter there are two 

 horn-like protuberances just back of 

 the frontal margin. The cephalic su- 

 ture is the same except that it is more 

 open at the bottom. The other pro- 

 tuberances and depressions of the head 

 are the same, except that in erosa, there 

 is a prominent tubercle between the 

 eyes and the front ; in S. pallida this 

 is lacking, or, if represented at all, by 

 a low swelling. All of the projections 

 of the head are more or less eroded. The segments of the thorax 

 have very low tubercles or slight swellings where the spines are situ- 

 ated in pallida. The rugse of the lowest portions of the thorax are 

 much more prominent in this species. In outline erosa is narrower 

 and less arcuate, the outer margins of the segments are much less 

 produced. The 7th segment is not noticeably wider than the base 

 of the abdomen. The abdomen holds its width to a point beyond 

 the middle, whence it is rounded to the terminus, which, as in 



Fig. 8. Synidotea erosa 



Benedict. 



r 



