274 A HISTORY OF RECENT CRUSTACEA 
with hairs on both edges. The molar tubercle, which in 
Mysis is large, has here become obsolete. The pleopods in 
the male are all natatory. The telson is truncate except in 
one species. ‘T'he type species, Mysidopsis didelphys (Nor- 
man), is British, as are also Mysidopsis gibbosa, Sars, and 
Mysidopsis angusta, Sars. All three are also Norwegian, 
and the last is unique in having no spines or teeth or setz 
within the cleft of the telson. Mysidopsis hibernica, Nor- 
man, 1892, has only been taken at Valentia in Ireland. 
Mysideis insignis, Sars, agrees with the preceding genus 
in having the pleopods of the male natatory, but differs in 
the mouth-organs, and in the very short incision of the 
telson it has two long plumoss sete. 
Leptomysis agrees with the two preceding genera as to 
the male pleopods, but agrees nearly with Mysis in the 
mouth-organs ; the scale of the second antenne is divided 
into two distinct segments, which are setose on both mar- 
gins. ‘The telson is tongue-shaped, with numerous spines 
about the apex, which is not incised. ‘Two of the species, 
Leptomysis lingvura, Sars, and Leptumysis gracilis, Sars, are 
British. Norman supposes Cynthia Flemingit, Goodsir, to 
be a synonym of the former. 
Hemimysis abyssicéla, Sars, is not far remote from Mysis, 
but among other differences has the fifth pleopods in the 
male well developed as swimming-organs. As a deep- 
water form itis distinct from most of the species of Mysis, 
which are littoral or sublittoral as a rule. 
Stilomysis grandis (Goés), formerly included in Mysideis, 
has the first, second, and fifth pleopods in the male similar 
to those of the female, but the third and fourth pairs with a 
stiliform outer branch. 
Pseudomysis abyssi, Sars, has the eyes quite rudimen- 
tary, without either pigment or visual elements. The scale 
of the second antenne is fringed with sets on both mar- 
gins. ‘The mouth-organs are like those of Mysideis. The 
legs are rather feeble, the sixth joint being much sub- 
divided, and the exopods unusually long. The auditory 
apparatus in the inner branch of the uropods is rudimen- 
tary. The telson is exceedingly short, lamelliform, and 
