On Platydor'inn. 421 



be absent or rare. Pleodorina caUfornica was extremely 

 abundant in Salt Fork in August, but had almost entirely 

 disappeared by the time that Platydorina had reached its 

 maximum. A few specimens of Volvox, which, in this locality, 

 is common in the spring months, were also noted, while 

 perhaps the most interesting associate in Salt Fork was 

 Ceratinm kiimaonense, discovered by Carter ('71) in Hindostan. 

 Other chlorophyll-bearing associates frequently seen are 

 Pediastriim, Scenedestnns, Actinastrum, and Closteriuni. 

 Among the diatoms, Melosira, Fragillaria, and Surirella, 

 were to be seen ; and among the Peridinidte, Peridinhvm 

 tahidatum was almost always represented. 



The zooplankton associated with Platydorina is not less 

 varied than the phytoplankton. The Protozoa were usually 

 represented by Arcella, Dijfiuyia, and occasionally by pelagic 

 Anuria; by Synura, Mallomonas, iJinohryon, and Uroglena ; 

 and by Codonella and Coleps. Among the Rotifera the order 

 Ploima was well represented ; Triarthra and the BrarJiionidce 

 — notably Brachionns m'ditarh, B. angidaris, B. piinctatus, and 

 B. bakeri, and its varieties — were most common during the 

 summer months, while the Synrh(etid(C increase in numbers in 

 the early autumn. Polyarthra was frequently abundant, and 

 Rotifer, Philodina , Asplanchna, Euchlanis, Cathypna, Distyla, 

 Monostyla, and Pterodina, were often represented by one or 

 more species. The paucity of Entomostraca stands in sharp 

 contrast with the abundance of rotifers, the former group 

 being represented by relatively few species and few adult 

 individuals. The nauplii of Cyclops were, however, as a rule 

 abundant, but only occasional specimens of adult Cyclops, 

 Diaptomus, Bosmina, Chydonis, Ceriodaphnia, Daphnia, and 

 Cypr'idopsis were to be seen. 



Platydorina raudata n. g., n. sp. 



The species here described consists of a horse-shoe shaped 

 coenobium or colony (PI. XXXVIIL, Fig. 1) of 16 or 32 

 bitiagellate cells, the anterior end corresponding to the toe of 

 the horse- shoe and the truncate posterior end to the heel, the 



