1927] Pilsbry-Bequaert, Lhe Aquatic Mollusks of the Belgian Congo 365 
Young specimens sometimes have several green rays, as in Plate 
XXVIII, fig. 2, but we have seen no adults so marked. , 
_ In some very old individuals (length, 145 mm.) there is a sharp- 
edged ridge or incipient septum over the anterior end of the beak cavity, 
such as is seen in well-characterized adult shells of Z. concamerata, 
but not so strongly developed as in old shells of that species. 
The few specimens from Katala, below Zambi, (Pl. XXVIT, fig. 2) 
are large, 100-110 mm. long,— with anteriorly glossy periostracum 
which in drying generally peels off in large part. The radial undulations 
of the typical form are wanting, or in some individuals weakly indicated. 
The usual dimensions and those of a long, compressed individual are: 
Length, 109 mm.; height, 85 mm.; diameter, 52.0 mm. : 
ft Ob gy oe 
Egeria congica was originally described from a left valve measuring: 
length, 25%mm.; height, 24 mm.; diameter (calculated for both valves), 
17mm. This could only be a young of Dautzenberg’s tuckeyi, of which | 
we have specimens of the same size and proportions. The description 
and the comparison with G. truncata Dunker fully supports this identifi- 
cation. C. R. Boettger (1913, pp. 90-91) was of opinion that it was a 
young specimen of G. duponti, a form which we cannot separate from 
tuckeyt. 2 | 
M. Dautzenberg appropriately named this fine clam after Captain 
J. R. Tuckey, R.N., leader of the first scientific expedition to the Congo. © 
It is noticed, if somewhat obscurely, in Tuckey’s narrative; moreover, 
some of Tuckey’s‘specimens were figured by Sowerby a few years later. 
It appears to be, thus, the first shell from the Congo River to be figured 
or noticed in any scientific work. It is unfortunate that Dautzenberg’s 
name must be relegated to the synonymy, since it would have reminded 
us of a brave man who lost his life in the exploration of the great river. 
Galatera dupontt Dautzenberg is a small, smooth form of congzca. 
Possibly in the type locality it has been stunted by unfavorably saline 
conditions, as the place is at the river’s mouth. At all events, the type 
figures can easily be matched exactly by many specimens found with 
typical tuckeyz and fully connected with that. One is illustrated in 
Plate XXVIII, figs. 1, la. : | 
Galatea rubrotincta Preston is merely a young H. congica which has 
not yet become sculptured. It is in the stage when the height slightly 
exceeds the length. | 
Egeria congica is, we believe, a well-marked species, entirely distinct 
from EH. paradoxa (Born). 
