398 MUSEO NACIONAL DE BUENOS AIRES. 
six segments of the thorax have the posterior margin produced 
backward in a median tooth, which increases gradually in size 
froms the first to the fourth, which is very large and then decrea- 
ses In size, the last two being about equal. The seventh thoracic 
segment 1s visible only on the ventral side. 
The abdomen is composed of four segments, the first thee of 
which are short and subequal in length. The lateral parts of the 
first segment are covered by the sixth thoracic segment; those of 
the second segment are produced a little beyond the post-lateral 
angles of the sixth thoracic segment; those of the third segment 
are short and are produced only a little distance. On all three seg- 
ments, there is a median tooth on the posterior margin, similar to 
those on the thoracic segments. The terminal segment has the 
sides slightly converging and terminating in an acute tooth on 
either side. The posterior margin 1s produced in the middle in a 
very obtuse angle. 'The dorsal surface is furnished on either side 
with a curving ridge, situated close to the anterior and lateral 
margins of the segment. Below this on either side is a second ridge 
originating near the middle of the segment and terminating a short 
distance from the lateral margin in an angular process. There is 
a small, flat angular process, one en either side of the median line 
near the base, where the second ridge originates. A long, promi- 
nent, acute spine is situated in the median line on the anterior 
portion of the segment. On the posterior portion of the segment 
is a ridge produced into three very long, acute, flat spines, vne in 
the median line and one on either side, the median spine being as 
long as the median spine anterior to it. The uropoda are similar 
in shape, the outer being smaller and shorter than the inner one, 
with the posterior extremity broadly rounded; they are inserted 
just within the lateral tooth of the terminal segment. The first 
pair of legs are subchelate with the propodus broadly oval. 
Six specimens, all females, were collected af the Sandwich du 
Sud in 1910 by Lahille. 
The type is in the Museum d'Histoire Naturelle de Paris. 
his speci:s is closest to Serolis schyt*ei Liitsken. *. 
1 Vidensk. Meddel. f. d. nat. Foren. i Kjobenhavn, 1858, p. 98, Taf. 1, figs. 12-13. 
