340 Annuls nf the Month African Museum. 



Specific Characters Female. Shell very tumid, seen laterally 

 almost circular in outline, with the dorsal margin boldly arched, the 

 ventral bulging in the middle, but nearly straight behind ; posterior 

 extremity narrowly truncated. Head rather procumbent, and termin- 

 ating in a slightly curved acute rostrum ; surface of valves sculptured 

 in their anterior part, with very distinct curved striae running parallel 

 to the anterior edges, the posterior part exhibiting a more or less 

 conspicuous reticulation ; infero-posteal corners armed with a distinct 

 curved denticle. Ocellus smaller than the eye, and located somewhat 

 nearer to it than to the tip of the rostrum. Antennulae comparatively 

 small. Lower expansion of the labrum securiform and having the 

 edge divided into four well-marked serrations. Tail-piece with the 

 distal part rather narrow and incised at the end ; supra-anal angle 

 considerably prominent, and occurring almost in the 'middle of the 

 piece ; marginal denticles well marked, about ten on each side, 

 the three posterior pairs more prolonged than the others ; apical 

 claws comparatively short, each with two unequal denticles at the 

 base. 



Colour dark yellowish -grey. 



Length of shell about <>3 mm. 



Remarks. This form was first described by Richard as a species of 

 the genus Pleuroxus ; but was subsequently referred by the present 

 author to the genus Chydorus, to which it evidently bears a much nearer 

 relationship, though differing in some points from the more typical 

 species of that genus. 



Occurrence. The present characteristic form was reared in con- 

 siderable numbers from the Kuysua mud, but did not develop from 

 any of the other parcels received. 



Distribution. Palestine, South America. 



40. CHYDORUS LEONARDI, King. 



Chydortis Iconardi, King. L.c. 1852, p. 258, pi. vii c. 



Remarks. This cosmopolitan species (not figured in the plates) 

 must also be included in the fauna of Cape Colony, as several speci- 

 mens were found in two alcoholic samples taken by Dr. Purcell from 

 ponds in the neighbourhood of Cape Town. The same form also 

 appeared abundantly in nearly all my aquaria, though an accidental 

 transfer together with the aquatic plants, which for the sake of 

 aeration of the water were introduced in them, was not excluded. By 

 most authors this form is regarded as only a small variety of the 

 common Chydorus sphaericus (Miiller). 



