26 G. 0. Sårs. 



being continued along the upper side of the posterior projec- 

 tion, hind edges quite smooth. Eye comparatively small; 

 ocellus extremely minute, sub-rhomboid in form. Caudal 

 part almost as in S. semiserratus, though the supra-anal pro- 

 jection appears somewhat less prominent, caudal claws with 

 a basal series of slender denticles, their distal part being- 

 only finely ciliated along the concave edge. Male resemb- 

 ling that of the preceding species, though easily distinguish- 

 able by the different shape of the head and by the very 

 prominent upper posterior corner of the carapace. Colour 

 of female yellowish, sometimes with 3 dark, irregular patches 

 on each side of the carapace. Length of adult female reach- 

 ing 2.30 mm., of male 0.80 mm. 



Remarks. — This form is undoubtedly identical with the 

 species recorded by Mr. Richard under the above name. It 

 is easily recognizable from any of the other known species 

 of this genus by the acutely produced, almost spiniform 

 posterior projection of the carapace. Before becoming 

 acquainted with Mr. Richard's paper, I had therefore assigned 

 to this form the name S. acutus. In habits it exactly agrees 

 with the preceding species. 



Occurrence. — I have also had occasion to examine 

 numerous specimens of this pretty form, both males and 

 females, reared in several of my aquaria prepared with mud 

 from Argentina. No specimens of this form on the other 

 hand, were raised from the Brazilian mud received. Yet its 

 occurrence in Brazil is stated by Mr. Richard, the specimens 

 examined by him being collected by Dr. v. Ihering at Rio 

 Grande do Sul. 



