62 Mr. H. B. Preston on 



foliaceous, and darker in colour posteriorly, both valves sculp- 

 tured with coarse concentric growth-lines ; umbones much 

 eroded, rather small ; dorsal margin somewhat arched ; ventral 

 margin slightly rounded ; anterior side rounded above, sloping 

 below; posterior side bluntly rostrate; anterior lateral teeth 

 very short ; posterior laterals long and straight, slightly 

 serrated ; cardinal teeth curved, massive, jagged, especially in 

 left valve ; anterior adductor scar deeply excavated, squarish ; 

 posterior adductor scar irregulai'ly triangular, not deeply 

 impressed ; interior of shell iridescent, pale pinkish, shading 

 to bluish white towards the ventral, anterior, and posterior 

 margins. 



Long. 21, lat. 37 mm. 



Hab. Shire' River, at a point from 3 to 4 kilometres to the 

 south of Lake Nyassa {Mgr. Leckaptois). 



Mutela opalescens, sp. n. (Fig. 12.) 



Shell moderately thin, irregularly rectangular, posteriorly 

 angled, covered with a thin olive-brown periostracum, sculp- 

 tured with fine irregular lines of growth and fine, transverse, 

 radiate stria?, which are more apparent anteriorly ; umbones 

 eroded, very small, flattish ; dorsal margin ascending, ante- 

 riorly straight, posteriorly very slightly curved at the top of 

 an almost wing-like expansion ; ventral margin scarcely 

 rounded, very slightly constricted towards the middle ; ante- 

 rior side short, descending obliquely, somewhat excavated ; 

 posterior side produced below, bluntly rounded ; hinge-teeth 

 obsolete ; adductor scars moderately impressed ; palleal 

 impression rosy, iridescent pink ; outer margins opalescent, 

 the radiate striae very noticeable in the interior of the shell. 



Long. 73, lat. 35 mm. 



Hab. Shire River, at a point from 3 to 4 kilometres to the 

 south of Lake Nyassa {Mgr. Leckaptois). 



In places where the periostracum is lacking, through process 

 of erosion, the shell appears to be highly iridescent. 



Mutela cuneata, sp. n. (Fig. 13.) 



Shell differing from M. opalescens by its narrower and more 

 elongate form, much more solid texture, and in the adductor 

 and other scars in both valves being much more deeply 

 impressed ; the interior of the shell is more nacreous and 

 presents a finely granular appearance, which is not the case 

 in M. opalescens ; moreover the transverse striae do not appear 

 in the interior of the shell as in that species. 



Long, (of type specimen) 36, lat. 81 mm. 



