A00 MUSEO NACIONAL DE BUENOS AIRES. 
the second and third abdominal segments !. The shape of the 
last abdominal segment is also different in the two species being 
less pear-shaped in the specimens from the Sandwich du Sud and 
truncate at the tip. Serolis convexa is described as being ofa 
uniform-pale brown color, while the specimens from the Sand- 
wich du Sud are uniforsuly white Serolis Gaudichaudii” Au- 
douin and Milne Edwards is another closely allied species. The 
new species agrees with the former in having the lateral ridges 
of the terminal abdominal segment very faint and in the more 
truncated tip. It differs, however, in the longer antennae; in 
Fig. 2,— Serolis laevis. x. 
having the last two segments of the thorax narrower than the 
preceding ones; in the absence of an epimeral suture on the fifth 
thoracic segment; in having the suture on the opercular valves 
more nearly transverse; in the different shape of the terminal 
abdominal segment; and in the almost complete absence of tho 
median keel, and in the different color, Serolis Gaudichaudii being 
described as dark brown and dotted all over with black spots of 
various sizes. 
1 This is true of Cunninghams figure, but in the specimens in the U. $. Nat. 
Museum and in Studer's figure, (Abhandl K. Akad. Missenschaften zu Berlin, 
1883 [1884), Taf 1, fig. 1.) the lateral angles of the sixth thoracic segment are lon- 
ger. Studer's figure does not show the median and lateral ridges on the terminal 
abdominal segment, so characteristic of this species. 
? Archives du Muséum d'Histoire Naturelle, n. 1811, pp. 22-25, pl. 1, 2, figs. 1-7. 
