386 Wisconsin Academy of Sciences, Arts and Letters. 



The heart as seen from the side, shows a tube convex below and con- 

 cave above. It is truncated anteriorly, and the aorta issues from its 

 ventral side. From above the heart closely resembles that of Latona y 

 having the form of a broad sac, rounded behind, and widest through the 

 venous ostia. 



The shell-gland has a form in this genus, which is unique among the 

 Cladocera. It consists of three branches, of which the shortest is dor- 

 sal and extends toward the heart, the next in length is ventral, while the 

 longest extends posteriorly and may reach through two-thirds of the 

 length of the valve. This last loop is found only in Latonopsis. The 

 whole gland consists of a tube doubled on itself, whose course can easily 

 "be traced. Beginning near the mandible in a bladder-like expansion the 

 tube passes into the valve and extends ventrally; it returns on itself to 

 the middle point, then passes backward in a long loop, returns again to 

 extend up toward the heart and come back to the middle. Then comes 

 a second posterior loop, lying parallel to and within the first, and on its 

 return the tube passes to its outlet near the mandible. Thus there are 

 two passages in the dorsal and ventral loops and four in the posterior, 

 not three as stated by Sars (op. cit. p. 9.). Sars' figure (PL I, Fig 1.) shows 

 the organ quite correctly. 



DESCKIPTION OF MALE. 



The male resembles in general the young female. 



The antennules are long and stout, being often nearly half as long as the 

 animal. They taper toward the apex, are curved, but not geniculate. They 

 are provided with a long row of very fine teeth extending from a point near 

 the sense-hairs to the apex. They thus resemble in general the antennule 

 of the male Sid a and Daphnella and differ widely from the male Latona. 

 Near the base of the antennule on the inner side is a stout projection, 

 rounded at the apex and covered with very fine hairs. This projection 

 is probably equivalent to the " appendix ciliata " of the male Latona.* 

 In Latona, Sars shows the appendix ciliata some way distal from the 

 olfactory hairs, while in Latonopsis, it is some way proximad to these. 

 My specimens of Latona, however, show'the appendix close the to sense- 

 hairs; so that the difference of position does not interfere with homol- 

 ogy. The cilia on the appendix of Latonopsis are very fine and easily 

 overlooked; they are far less conspicuous than in Latona. 



The copulatory organs resemble those of Latona. They are a pair of 

 long, curved, flexible appendages, perforated by the vasa def erentia. 

 They arise at the base of the post-abdomen and are long enough to reach 

 beyond the terminal claws. 



The first leg shows a very distinct and strong hook. In this structure 

 Latonopsis differs from the other Sididoz and especially from Latona. 



* Sars,*0. O. Norges Ferskvandskrebsdyr. j Cladocera Ctenopoda, p. 55. PI. Ill, Fig. 17. 



