274 A HISTOBY OF EECENT CEUSTACEA 



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. The 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 setae 

 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 plumose setas. 



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 antennas 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 Leptomysis gracilis, Sars, are 

 British. Norman supposes Cynthia Flemingii, Goodsir, to 

 be a synonym of the former. 



Hemimysis abyssicola, 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 it is distinct from most of the species of Mysis, 

 which are littoral or sublittoral as a rule. 



Stilomysis grandis (Goes), 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. TJie scale 

 of the second antennas is fringed with setas 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 



