200 CALIFORNIA ACADEMY OF SCIENCES. 



ing abdominal segment. The margins are furnished with 

 several irregularly spaced spines, and the tip is slightly 

 emarginate. The inner ramus of the uropods is expanded 

 at the base, where the auditory organ is located, whence 

 it tapers to an acute tip. The outer ramus is much longer 

 than the inner one, the sides sub-parallel to the rounded 

 tip; both sides of both rami are furnished with long, 

 plumose setae. 



The specimens (in alcohol) were almost colorless, with 

 the exception of several large, irregularly branching pig- 

 ment spots. Length of largest specimen x / 2 in. 



The specimens upon which this species is founded were 

 collected at Lake Merced, California, October, 1895, by 

 Dr. H. P. Johnson, to whom I am indebted for the oppor- 

 tunity of making this description. There were thirteen 

 females and but one male in the collection. One female 

 had the marsupial pouch filled with young embryos; the 

 other females were mostly of smaller size, with the mar- 

 supial lamellae undeveloped. This species is closely allied 

 to Murdoch's Mysis ray/'/, from northern Alaska. It 

 differs, however, in the form of the rostrum, which is not 

 quadrangular but rounded, and does not extend nearly so 

 far forward as the middle of the optic peduncles. The 

 margin of the telson is entirely devoid of seta?, while the 

 apex in Jlf. rayii is " fringed " with them. 



EXPLANATION OF FIGURES. 



First antenna of a male, showing the club-shaped sense organ. 

 Second antenna. 

 Mandible. 



Maxilliped, or first thoracic appendage. 

 Second thoracic appendage. 

 Last thoracic appendage. 

 Fourth pleopod, male. 

 Fifth pleopod, male. 

 First pleopod, male. 

 Fig. 10. Uropods and telson. 

 All the figures were drawn to the same scale. 



