60 Mr. II. B. Preston on 



Unio char on, sp. n. (Fig. G.) 



Shell elongately ovate, slightly gaping at both sides, 

 covered with a black periostracum, corrugately sculptured 

 towards the umbonal region and marked below with irregular 

 concentric ridges ; urn bones eroded, moderately large, not 

 prominent; dorsal margin curved; ventral margin slightly 

 constricted in the middle, otherwise straight; anterior side 

 rather produced, angularly rounded ; posterior side elon- 

 gately produced, sharply rounded ; lateral teeth in both valves 

 elongate, curved; cardinal tooth in right valve elongate, 

 lather fine, rising considerably in the middle; cardinal tooth 

 in left valve almost obsolete, serrated anteriorly ; anterior 

 adductor scars deep, somewhat square in shape ; posterior 

 adductor sears scarcely impressed ; interior of shell nacreous, 

 bluish white. 



Long. 2lr5, lat. 52 mm. 



Hab. Silongwe, British Central Africa. 



Unio vicinus, sp. n. (Fig. 7.) 



Shell differing from U. charon by its narrower form and 

 somewhat more acuminate posterior side, lighter texture, 

 much smoother concentric sculpture, and paler colour, the 

 periostracum being of a pale yellowish-brown colour; the 

 muscular scars are much larger, and, in the case of the ante- 

 rior adductor, more deeply impressed. 



Long. 24, lat. 52 mm. 



llab. Silongwe, British Central Africa. 



Unio choziensis, sp. n. (Fig. 8.) 



Shell small, squarely ovate, moderately convex, covered 

 with a blackish-brown periostracum, sculptured with fine 

 concentric strias and rather coarse, transverse, corrugated 

 ridges, which become finer posteriorly ; umbones not promi- 

 nent ; dorsal margin sloping in an anterior direction ; ventral 

 margin slightly rounded ; anterior side descending somewhat 

 abruptly; posterior side rather acuminately rounded; lateral 

 teeth elongate, straight ; cardinal tooth in right valve weak, 

 jagged, erect anteriorly, bifurcate posteriorly ; cardinal teeth 

 in left valve elongate, finely jagged, cleft anteriorly ; muscular 

 scars deeply impressed anteriorly, scarcely apparent poste- 

 riorly ; interior of shell iridescent, bluish white. 



Long. 16'25, lat. 25 mm. 



Hab. Chozi River, a tributary of the Chambzi, flowing 

 into Lake Bangweolo from the east. 



