950 NODULARIA 
and extending in many cases over a part or all of the disk; 
right valve with two, usually compressed, pseudocardinals, one 
above the other, the lower the more elevated, separated by a 
parallel-sided socket, and having one lateral; left valve with 
two compressed pseudocardinals, both in front of the beaks, 
and two laterals; cavity of the beaks moderate, not compress- 
ed; anterior muscle scars deep, posterior shallow; nacre white. 
Animal (of N. japanensis and N. e@quatoria) having the 
inner gills alone filled throughout their entire length with ova, 
forming a pad-like marsupium, united to the abdominal sac 
or free from it. 
Type, Unio douglasie Gray. 
The genus Nodularia was established by Conrad in 1853 in 
the Proceedings of the Academy of Natural Sciences of Phil- 
adelphia with Unico douglasie Gray as the type. The name 
Lanceolaria, with Unio grayanus Lea as its type, was given 
by Conrad a few lines above this on the same page, but as he 
used this name only in a subgeneric sense I think that the 
name Nodularia should be used for the genus. In his descrip- 
tions of the two groups on the following page Nodularia is 
placed first. 
I have placed under this name a large number of species 
from southeastern Asia and Tropical Africa, which are fairly 
typified by the Unio douglasie of Gray. In general the shells 
are small to moderate in size, only one species, U. anodonte- 
formis, becoming large. The structure is usually rather light, 
the hinder end is nearly always pointed. The posterior base 
of almost every species is more or less inflated, as are the fe- 
male shells of many species of Lampsilis. Generally the form 
varies from tong elliptical or ovate to very long. The beaks 
are usually sculptured with zigzag-radial ridges and in a ma- 
jority of the species this sculpture extends over the disk to a 
greater or less degree, often breaking up into nodules or gran- 
ulations. In such species as U. crispisulcata, the sculpture of 
beaks and disks is almost strictly radial, showing, however, 
slight zigzags and standing as a connecting link between the 
