ORTMANN: A MONOGRAPH OF THE NAJADES OF PENNSYLVANIA 333 
alike; there are very few minor differences, but the genera, Obliquaria and Cypro- 
genia, stand out more prominently among them." They possess a remarkably 
small number of ovisacs, which stand rather in the middle of the outer gill, and 
the shell also is peculiar in its shape and ornamentation. Cyprogenia is in addition 
distinguished by the great prolongation of the marsupium, which forces it to coil 
up within the shell. Thus these two genera are well defined. 
As has been seen above, there is among the Lampsiline a further differentia- 
tion connected with the sexual apparatus, which, in my opinion, is of prime value. 
This is the development of special structures on the edge of the mantle in front of 
the branchial opening. Although some of these structures have been noticed by 
previous writers, no importance has been attached to them. 
We have observed, that in the genera Truncilla, Micromya, and in certain 
species of Lampsilis such structures are present, while in other species of Lamipsilis, 
as well as in Obovaria, Plagiola, Obliquaria, Cyprogenia, and Ptychobranchus, they 
are absent, or barely indicated. We have seen, that Ptychobranchus, Obliquaria, 
and Cyprogenia may be distinguished on other grounds. This leaves certain species 
of Lampsilis (ligamentina, alata, gracilis), and the genera Obovaria and Plagiola as 
a group, possessing a similar conformation of the edge of the mantle. Plagiola, 
Obovaria, and Lampsilis ligamentina are practically identical in the entire structure 
of the soft parts, and in the form of the shell they also stand rather close together. 
With regard to Lampsitlis ligamentina, I do not see any reason why it should not 
be placed with Obovaria; in fact it fully agrees with Simpson’s diagnosis of Obovaria, 
and could be grouped very well with O. ellipsis. Plagiola can be distinguished 
from Obovaria only by the characters of the shell, chief among which are the presence 
of a distinct posterior ridge and the peculiar markings of the epidermis. (In ad- 
dition, P. securis has a peculiar glochidium, but the writer does not know whether 
this glochidium is found in other species of Plagiola.) 
Lampsilis alata and gracilis have been placed by Simpson in a separate sub- 
genus, Proptera, on account of the peculiarities of the shell (general shape and 
character of hinge-teeth). Sterki has proposed to elevate it to the rank of a 
genus on account of the odd glochidium of L. alata, assuming, that this shape is 
also found in the other species of Proptera. Since I have shown, that the glochidium 
of L. gracilis differs fundamentally from that of L. alata, and also from all other 
Lampsiline, we are forced to restrict the genus Proptera to those forms, which 
have a glochidium like L. alata (purpurata, levissima), and should create a new 
Recently, Sept. 24, 1910, I found a gravid female of Cyprogenia irrorata in the Ohio River at Portsmouth, Scioto Co., 
Ohio, and had a chance to study its soft parts. 
