66 G- O. Sars. 



tional species has as yet been recorded, and I am induced 

 to regard even the Brazilian form found in my aquaria as 

 only a variety of the European form. 



33. Gtraptolefceris testudinaria (Fischer). 



var. occidentalis. 

 (PI. X, figs. 8. a— a). 



Remarks. — The only difference I can detect be- 

 tween this and the well-known European form, is that the 2 

 denticles at the infero-posteal corners of the valves (see figs. 

 8, 8 b) are of far inferior size and less divergent. A similar 

 variety seems also to occur in North America, to judge from 

 the figures given by Mr. Herrick. 



Occurrence. — This form was not unfrequently 

 found in the aquaria prepared with mud from Sâo Paulo. 

 The specimens were easily detected, even without the aid 

 of the dipping-tube, owing to their peculiar habit of attaching 

 themselves to the walls of the aquarium, and resting in this 

 attitude for several time, thus admitting of being directly 

 examined with a strong magnifying-glass. 



Distribution. — Apart from Europe, this form has 

 been recorded from North America, Ceylon, Asia, Iceland, 

 Greenland, and the Azores. 



Gen. Chydorus, Baird. 



Remarks. — The species of this genus are easily 

 recognizable by the more or less globular form of the body, 

 and the peculiar revolving movements of the animal. Of the 

 numerous species described (about 20), the greater number 

 are so closely allied, as only to be distinguished by a 



