148 



(Paradoxostoma) had been established by S. Fischer on account of some per- 

 plexing peculiarities found in the structure of the oral parts. All these genera 

 have been admitted by subsequent authors, and their number has in recent 

 time been still more increased, especially by G. W. Mtiller, amounting at pre- 

 sent to about 30 in all. Owing to this considerable number of genera, it 

 would seem to be very desirable, that a grouping of them within subfamilies 

 should be effected, as done In the family Cypridse, and indeed some slight 

 attempt to do so has been made by a few authors. Thus in the year 1889 

 Brady and Norman discarded wholly from the other Cytheridae the genus Para- 

 doxostoma of Fischer as the type of a distinct family, Paradoxostomalidce. 

 G. W. Miiller has accepted this group, but rightly reduce its systematic rank to 

 that of a subfamily of the Cytheridae. The said author mentions also another 

 subfamily under the name of Cytherurince, but the exact limits of this sub- 

 family is not clarly indicated, nor has any further subdivision of the family 

 been effected. I have endeavoured in the present Account to carry out the 

 classification of the present family in a more complete manner, grouping the 

 several genera into 7 subfamilies, the characters of which will be exposed in 

 the sequel. 



Subfam. 1. Limnicytherinae. 



Characters of the subfamily, Shell in most cases of rather feeble con-, 

 sistency, scarcely at all calcareous, and only faintly sculptured. Hinge imperfect. 

 Valves subequal, with the marginal zone crossed by scattered simple pore-chan- 

 nels. Only a single eye present, as in most Cypridae.--Both pairs of antennae di- 

 stinctly geniculate and subpediform; the anterior ones with the terminal part 

 firmly connected with the distal segment of the basal part, and generally com- 

 posed of 3 joints armed with scattered spiniform setae. Posterior antennae with 

 the flagellum well developed in both sexes. Mandibular palp short and stout, 

 distinctly triarticulate and having the vibratory plate rather fully developed. 

 Legs not much different in length an generally of same appearance in the 2 

 sexes. Caudal rami of somewhat different structure in the different genera. 



Remarks. The Cytherids comprised within this subfamily are all true 

 freshwater forms, and have generally been referred to a single genus, Limni- 

 cythere. Kaufmann has however distinguished another riearely allied genus 

 Leucocythere, and a 3rd genus, apparently referable to the same subfamliy, 

 has recently been established by the present author under the name of Gom- 



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