1927] Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 443 
Subgenus PLE1opon Conrad 
Pleiodon Conrad, 1834, Journ. Ac. Nat. Sci. Philadelphia, VII, p. 178. Mono- 
typic for Pletodon macmurtreit Conrad = Iridina ovata Swainson. 
Pliodon BoureuienatT, 1879, ‘Descript. Moll. Egypte,’ p. 44. Emendation of 
Pleiodon Conrad. 
The following species have been described: 
Tridina (Pleiodon) ovata Swainson = Iridina ovata Swainson, 1823, Philos. Mag. 
and Journ., LXI, p. 118 (mo type locality given). Rrrve, 1841, ‘Conchol. System.,’ 
I, p. 122, Pl. xc11t. Pleiodon ovatus Stmrson, 1914, ‘Descript. Cat. of Naiades,’ p 
1376 = Pleiodon macmurtrei Conran, 1834, Journ. Ac. Nat. Sci. Philadelphia, VIT, 
p. 180, Pl. x111 (Liberia). Platiris (Iridina) leati “Sowerby” I. Lea, 1852, ‘Synopsis 
of Naiades,’ p. 54. Iridina splendida CuEnv, 1858, ‘Illustrations Conchyl.,’ Iridina, 
Pl. 1, figs. 2 and 2a-e. 
Tridina (Pleiodon) diolibana (Bourguignat) =Pliodon diolibanus BoURGUIGNAT, 
1879, ‘Descript. Moll. Egypte,’ p. 47. Exact locality unknown (either from the 
Niger, Senegambia, or Gambia). 
Tridina (Pleiodon) elongata (Bourguignat) =Pliodon elongatus BouRGUIGNAT, 
1879, ‘Descript. Moll. Egypte,’ p. 47. Exact locality unknown (probably from the 
Upper Senegal). 
Tridina (Pleiodon) letourneuxiana (Bourguignat) =Pliodon letourneuxianus ° 
BovurGuicNnat, 1879, ‘Descript. Moll. Egypte,’ p. 48. Exact locality unknown 
(probably from the Upper Senegal). 
Tridina (Pleiodon) pachyodon Bomtieea = Pliodon pachyodon BOURGUIGNAT, 
1879, ‘Descript. Moll. Egypte,’ p. 46. Pliodon ovatus var. pachyodon GERMAIN, 
1909, Arch. Zool. Expér. Gén., XLI, pp. 44 and 59, fig. 41. Pletodon ovatus var. 
pachyodon Simpson, 1914, ‘Descript. Cat. of Naiades,’ p. 1377. Exact locality un- 
known (either from the Niger, Senegambia, or Gambia). 
# 
Hyriine 
PSEUDOSPATHA Simpson 
Burtonia Boureuienat, 1883, ‘Moll. Fluv. Nyanza Oukéréwé,’ p. 20. Mono- 
type: Spatha tanganyicensis E. A. Smith. Preoccupied by Burtonia Bonaparte, 
1850. | 
Pseudospatha Simpson, 1900, Proc. U. 8. Nat. Mus., XXII, p. 577. Substitute 
for Burtonia Bourguignat. Type by original designation: Spatha tanganyicensis EH. 
A. Smith. | 
Thin, strongly compressed, polished, yellow mussels, with the low beaks near the 
anterior fourth, and winged in front and behind; beaks either nearly smooth or un- 
dulate and pustulate, often retaining the circular glochidial shell. The hinge-plate 
has an angular or narrowly raised edge, diverging forward and back from the beaks, 
and similar in both valves. The muscle scars are scarcely impressed, the foot pro- 
tractor apparently not distinct from the anterior adductor scar. 
The genus is only known from Lake Tanganyika. Burtoma carrer 
Putzeys, of the Congo River, isa M utela of the subgenus Chelidonopsis. 
