78 G. O. Sars. 



Biological Observations. — I only found this 

 form in one of my aquaria, and there not in any considerable 

 number. The specimens were, however, easily observable by 

 their extremely rapid movements, which were effected in abrupt 

 bounds. At times they were seen attached to the walls of the 

 aquarium, and in such cases could easily be taken up by the 

 aid of the dipping-tube. No male specimens were found. 



Occurrence. — The aquarium in which this form 

 appeared, was prepared with mud from the neighbourhood 

 of Sâo Paulo. 



Distribution. — The specimens examined by Dr. 

 Vàvra were taken in some ditches at Valdivia, Chili; the 

 solitary specimen examined by Mr. Richard was likewise 

 from that country. 



Gen. Pleuroxus, Baird. 



Syn: Rhypophilus, Schoedeler. 

 Remarks. — About 20 species of this genus, which 

 is easily recognizable by the more or less triangular form of 

 the carapace, and the greatly produced rostral projection, have 

 been recorded from different parts of the world. They may 

 conveniently be divided into 2 groups, according to the 

 structure of the caudal part. In the one group, of which 

 P. trigonellus (Müller) is the type, this part is rattier broad, 

 and peculiarly transformed in the male; in the other group, 

 of which P. lævis G. O. Sars is the type, it is much narrower, 

 tapers distally, and is less conspicuously transformed in the 

 male. The South American species, to be described below, 

 belong to the latter of these 2 groups. Two additional new 

 species of this genus have recently been recorded by Dr. 

 Ekman from Patagonia. 



