1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 367 
Young specimens of this species resemble the adult form closely in 
proportions. Two measure: 
Length, 18.0 mm.; height, 13.0 mm.; diameter, 8.3 mm. 
2 16,5 sg 12.0 arene oC: 
This species varies toward a higher, more trigonal shape, such as are - 
shown in Pl. X XIX, figs. 2 and 3, theother characters remaining the same. 
Length, 47.0 mm.; height, 33.0 mm.; diameter, 21.0 mm. 
45.0 saree oe = 20.4 
a od eo is 19.0 
Egeria nux, new species 
Plate X XIX, Figures 4-7 
Malela (Lang and Chapin Coll.). 
The shell is triangular, plump, very solid, covered with a smooth ecru-olive to 
buffy olive periostracum, often with small dusky spots, or rarely interrupted dark rays. 
The obliquely truncate posterior end is somewhat convex with a slightly concave, ill- 
defined escutcheon. No lunule. The anterior end is rounded, the outlines between 
ends and beaks slightly convex. The beaks are rather depressed, not very prominent. 
Fig. 82. Egeria nux Pilsbry and Bequaert. Radially corrugated individual. 
The interior is white (or sometimes more or less extensively violet on the lateral mar- 
gins, posterior region and basal margin). Hinge-plate strongly developed, the median 
cardinal tooth of the right valve narrowly triangular with bifid summit; in the left 
valve only the trace of a median tooth. Beak cavities moderately deep. Nymphs are 
very short and small. 
Length, 36.7 mm.; height, 29.3 mm.; diameter, 22.0 mm. Type; Pl. XXIX, Fig. 4. 
eae sa | SS" posers: = 25.0 Paratype. 
es 32.0 aire es ot 21.2 " 
In shape this small species is quite unlike the young of &. congica. 
It is much more nearly related to H. tenuicula (Philippi), but the outline 
is more triangular and the valves and teeth are much heavier. In £. 
truncata (Dunker) the beaks are narrower and the teeth are far heavier. 
