l86 M. M. SCHEPMAN, LAND- AND FRESHWATER MOLLUSCA ETC. 



many of them are only loose valves, so they may hâve been drifted together from several parts 

 of the river, which may account for the diversity of forms found in the same lot, without the 

 possibility to separate them in well-characterized varieties. The posterior or the anterior part 

 is often more truncated, than in the original figure, the shell consequently shorter, the ventral 

 margin is in many instances straighter, rarely as much rounded as in the type; some shells 

 are more swollen or flatter than usual, the hinge is variable in strength and length of the 

 cardinal teeth, partly on account of the érosion of the umbones; the colour of the interior 

 differs from nearly totally white to nearly quite violaceous, especially in very young spéci- 

 mens, with many intermediate ones ; old shells are mainly darker externally than young ones, 

 as is usually the case. 



One of the allied species is B. humerosa Desh. (Journ. de Conch. Vol. IX, 1861, p. 38, 

 PI. 2, fig. 1), but that shell is considerably more elongate, its ventral margin straighter, its 

 posterior part more truncated below, however a few old valves come very near to it, though 

 always shorter. A comparison with the types of thèse two species and of B. corbuloides Desh. 

 should be very useful, to clear up their affinities. If one had to compare only a few selected 

 spécimens of the forms under considération, it would not be difficult to erect several well 

 characterized species. 



Fam. UnIONIDAE. 



Unio Retzius. 

 1. Unio sp.? 



New Guinea. Sabang Camp, Jan. 20 — 30, 1907. 



Only one right valve has been collected, which I thought might belong to U. beauforti 

 Bavay, but there are too many différences with co-types I got for comparison from the 

 Zoological Muséum at Amsterdam, collected at the Sentani-lake and the Jamur-lake, that, 

 though those spécimens vary considerably, I could not identify it. As I could not décide from 

 this single valve, to which of the many gênera, in which the genus Unio has been split, it 

 may" belong, I hâve used the old name Unio, as Bavay has done (Nova Guinea, Vol. V, 

 Zool., p. 291). 



Virgus Simpson. 



1. Virgus lorentzi n. sp. PI. VII, fig. 2. 



Shell elongate, tongue-shaped, compressed, rather strong, dark brown. Anterior upper 

 margin nearly straight, but slightly convex, running with a rounded angle into the moderately 

 rounded anterior margin, which runs imperceptibly into the ventral margin, this latter is slightly 

 concave near the middle, then slightly decurvate and with a convex outline, running roundedly 

 into the posterior part of shell ; posterior upper margin slightly convex at first, then with a 

 blunt angle more than half way the length between umbones and posterior extremity; behind 

 this angle the margin is conspicuously but not strongly concave. Umbones low, eroded, slightly 

 pointed, placed at about '/ G °f the total length of shell, behind the umbones with traces of 

 short radiating plicae, more conspicuous on the right valve. Surface practically smooth, but 

 the slightly compressed, elongately triangular area is limited by a conspicuous ridge, moreover 



