36 G- O. Sars. 



the females, and were often seen in ardent pursuit of the 

 latter. 



Occurrence. — The aquaria in which this form 

 developed, were prepared with mud from 4 different locali- 

 ties, viz., Sâo Paulo, Itatiba, Ipiranga, and Argentina. 



12. Macrothrix sqvamosii, n. sp. 



(PI. VI, figs. 10—12). 



Specific Characters. — Female. Carapace 

 seen laterally, rounded triangular, scarcely longer than it is 

 high, dorsal margin considerably arched behind, ventral angu- 

 larly curved in front of the middle, posterior extremity ob- 

 tusely pointed. Head rather large, and not defined above 

 from the carapace by any depression, cervical organ incon- 

 spicuous, dorsal margin evenly curved and not bulging at 

 all in the ocular region, rostral projection somewhat pro- 

 duced, though obtuse at the tip, ventral margin perfectly 

 smooth. Surface of shell sculptured, especially towards the 

 dorsal face, with densely set squamiform ridges, giving the 

 dorsal margin of the carapace, and partly also that of the 

 head, a jagged appearance; lower edges of valves armed as 

 usual. Eye of moderate size; ocellus comparatively larger 

 than in the preceding species. Antennulæ not much elongated, 

 slightly widening distally, anterior face with about 5 trans- 

 verse rows of small spikes, posterior with a bunch of rigid 

 hairs near the tip. Antennæ about as in the preceding species. 

 Epipodites of 1st and last pairs of legs larger than in the 

 other pairs, though not nearly attaining such a development 

 as in M. elegans. Caudal part comparatively short, the 

 basal portion carrying the caudal setæ being far less pro- 



