ORTMANN: FAMILIES AND GENERA OF NAJADES. 285 
anterior end. Posterior margins of palpi connected for not quite 
one-half of their length. 
Fic. 12. Arcidens confragosus (Say). Male from Bayou Pierre, De Soto Parish, 
Wa. (Carns Mus: No. 62, 4,701.) 
Gills anodontine in structure. Simpson (1900), p. 661) describes 
the marsupium in peculiar terms (‘‘of a peculiar, granular texture’’). 
Although I have not seen gravid 
females, the sterile females I 
possess offer nothing unusual or 
different from other Anodontine. 
Only the outer gills are marsu- 
pial, and their septa are much 
crowded, forming very narrow 
water-tubes, while in the inner 
gill the septa are much more 
distant. The septa of the outer 
gills are typically anodontine, 
and an indication of secondary 
water-tubes is present in the 
sterile female (see pla ec VITT, Fic. 12a. Left gills of a sterile fe- 
fig 6) Besides, at the edge of male, from Pearl River, Jackson, Hinds 
: ¢ : Co., Miss. Carn. Mus., No. 61, 4,928. 
the marsupial gill, there is a SING ue aa ante £928) 
thick mass of tissue, which indicates, that in the gravid female the 
edge is capable of distending. 
