410 Bulletin American Museum of Natural History — (Vol. LIII 
Pliodontide A. T. pp RocHEBRUNE, 1904, Bull. Mus. Hist. Nat. Paris, p. 342. 
Shell resembling that of the Unionide. In the African forms the teeth, when 
present, are taxodont. The beak-sculpture affords no reliable family-characters, 
since some specics of Aspatharia have a zigzag sculpture similar to that of certain 
Unionide. 
“Diaphragm complete, formed anteriorly by the gills, posteriorly by the mantle. 
Anterior end of inner gill in contact with the palpi. Branchial and anal siphons 
sharply separated from one another; the canal open or closed above, but there is never 
a supra-anal opening. Gills with very indistinct and intercommunicating water 
tubes, or with well-developed water tubes. Marsupium only in the inner gills” (A. 
E. Ortmann, 1911, The Nautilus, XXIV, p. 129). Labial palpi large, rounded below. 
Dicecious so far as known. 
The Mutelide have been divided by Ortmann! into two subfamilies, 
as follows. 
MuvTELIN«#, in which the marsupial gill has well-developed, continu- 
ous septa forming well-defined water tubes, the non-marsupial gills 
also with distinct water tubes. The larva is a lasidium in the South 
American Anodontites, but is unknown in African genera. This group 
comprises genera with anodont or taxodont hinges. 
 Hyruna, having interlamellar connections interrupted, standing in 
rows, forming incomplete, communicating water tubes in the marsupial 
gills, the non-marsupial with poorly developed, scattered interlamellar 
connections. The larva is a glochidium. This subfamily comprises four 
South American genera having schizodont hinges. We provisionally add 
the African Pseudospatha. 
Among the African Muteline the chief divergence in anatomic struc- 
ture as now known is in the degree of concrescence of the margins of the 
mantle, as follows. 
I.—Mantle concrescent below the branchial orifice for one-fourth to 
about half of the basal length. Genera Mutela and Iridina. 
Mutela rostrata: about half of the lower margins concrescent. See Troschel, 1847, 
Archiv f. Naturgesch., XIII, 1, p. 278; Clessin, 1875, Malakoz. Blatter, XXII, pp. 
24—25, Pl. 1, fig. (as Iridina celestis Lea). 
Mutela (Chelidonopsis) hirundo and carrei: nearly half of the lower margins con- 
crescent. ‘See Germain, 1909, Arch. Zool. Expér. Gén., XLI, pp. 4-34. 
Mutela nilotica: margins concrescent for at least one-third of the lower border. 
See Deshayes, 1827, Mém. Soc. Hist. Nat. Paris, III, pp. 1-16, Pl. 1; Rang, 1835, 
Nouv. Ann. Mus. Paris, IV, pp 315-316. 
Tridina (Cameronia) spekit: one-fourth of the lower margins concrescent. See 
Pelseneer, 1886, Bull. Mus. Hist. Nat. Belgique, IV, pp. 116-128. 
1A. E. Ortmann, 1911, The Nautilus, XXIV, p. 130. 
