1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 387 
Unio Retzius Ps 
Unio Rerzius, 1788, ‘Diss. Hist. Nov. Test. Gen.,’ p. 16. Type: Unio tumidus 
Retzius. 
Nodularia ConraD, 1853, Proc. Ac. Nat. Sci. Philadelphia, VI, p. 268. Mono- 
type: Unio douglasie Griffith and Pidgeon. 
A. E. Ortmann (1918, The Nautilus, XX XI, pp. 128-131) has shown 
that Nodularia is a synonym of Unio. The African species placed by 
Simpson in Nodularia appear to belong to Celatura and Parreysia. 
The genus as at present defined inhabits Europe, Asia and Africa. 
All the tropical and South African forms belong to the opens Cafferia, 
which was erected by Simpson as a section. 
Subgenus CarreRia Simpson 
Nodularia section Cafferia Stmrson, 1900, Proc. U.S. Nat. Mus., XXII, p. 824. 
Type by original designation: Unio caffer Krauss. 
Unio section Cafferia Simpson, 1914, ‘ Descript. Cat. of N aiades,’ p. 574. 
‘Shell elongated or elliptical, rhomboid when old, solid; beaks full, the sculpture 
corrugated zigzag, the ridges often extending over the Re epidermis yellowish- 
brown to nearly black, dull colored, somewhat sulcate; teeth rather strong; muscle 
scars deep, well defined’”’ (Simpson, 1914). , 
This group was at first regarded by Simpson as a division of No- 
dularia; but having had later an opportunity of examining gravid 
specimens of one of the species, he found that it was a Unzo. 
Cafferia appears to be strictly African. Many of the South African 
forms belong here, but none are known from within our territory. 
A. E. Ortmann, who has examined the soft parts of Unio caffer, 
states that they differ little from those of Unio pictorum. The gravid 
females collected in Natal, in July, had mostly eggs, but one of them had 
glochidia. Of specimens obtained near Pretoria, Transvaal, in April, 
only one female was gravid and also had glochidia. The anatomy is 
described as follows: 
Anal opening separated from the supra-anal opening by a moderate mantle 
connection, slightly shorter than the anal. Supra-anal about as long as or slightly 
longer than the anal. The latter with the inner edge almost smooth. Branchia 
opening with distinct papille. No differentiating structure on mantle-edge in front of 
branchial. Palpi subfalciform, of medium size, their posterior margins united for 
nearly half their length. Gills of the unionid-type; gill diaphragm complete, sepa- 
rating anal and branchial openings. Anterior end of inner gills widely remote from 
the palpi. Inner lamina of inner gill free from abdominal sac, except at anterior 
end. Septa and water-tubes present, the former continuous and not interrupted, 
parallel to the gill-fillaments. In the male, and in the inner gill of the female, they 
are weak and distant from each other. The outer gill of the female is marsupial prac- 
tically in its entire length, with heavy and crowded septa. 
