List of Crustacea Cladocera from Madison, Wis. 387 



Sida, Limnosida and Daphnella have short, fleshy knobs rather than 

 nooks, and Latona is devoid of any special structure. Holopedium has 

 a hook similar to that of Latonopsis but much longer, as is natural in 

 that genus. 



The new hatched male has the copulatory organ in the form of a pair 

 of small buds, which do not reach the adult form until after four or five 

 moultings. The antennule of the young male differs widely from the 

 adult form. It is short, lacks the appendix ciliata, and shows a distinct 

 suture between base and flagellum. The latter is covered with long stragg- 

 ling hairs. The whole structure closely resembles the female anten- 

 nule. It is clear that the extension of the male antennule beyond the 

 sense-hairs in the homologue of the flagellum of the female. 



RELATIONS OF THE GENUS. 



Sars was entirely justified in separating Latonopsis from Latona. While 

 the structure of the two genera is quite similar in the female, the male 

 differs widely from that of Latona. The antenna is more like that of 

 Daphnella than that of any other genus, especially in the rami, while the 

 great development of the base is like that of Latona. The antennule is 

 peculiar and shows an intermediate stage between that of Latona and 

 Daphnella, though nearer the former. In the male, however, the anten- 

 nule is more like that of Sida than that of Latona. In the form of the 

 body, the outline of the head, in the fornices, the position of the eye, 

 eye-muscles and optic ganglion; in the heart; in the shape of the cara- 

 pace, and the development of the setae of the carapace, it approaches 

 Latona. It lacks entirely the peculiar development of the antenna seen 

 in Latona and [the plate on the lower side of the head; while Latona 

 lacks the development of the shell-gland, which Latonopsis shows. In 

 most of the points of resemblance and difference between the two 

 genera, Latonopsis is nearer the ordinary form of the Sididaz, and it 

 may be considered as connecting Latona with the other Sididai, but 

 with many cross-relations to other genera. 



RELATIONS OF THE TWO SPECIES. 



L. oecidentalis is very close to L. australis. Indeed, I am not sure but 

 that they are really the same species. There are many points of minor 

 difference, but the most tangible is the antennule, which is about twice 

 as long in the American form. It must not be forgotten, however, that 

 Sars' specimens were hatched from mud, and it may be possible that 

 specimens collected in their native waters will agree more closely with 

 the American species. If the difference is constant, L. australis is nearer 

 the ordinary type of the Sididoz in the structure of the antennule. 



