ORTMANN: A MONOGRAPH OF THE NAJADES OF PENNSYLVANIA 301 
And indeed I have seen the hooks in the two last-named species. Lea himself 
in the case of Hemilastena suggests that the glochidia he has seen are too young, 
and that the hooks might develop later. And this is apparently true, for I have 
observed in a number of species, that young glochidia have no hooks, while they 
are present in older ones. In the following cases this was most evident: specimens 
of Alasmidonta marginata, collected Sept. 2, 1907; of Alasmidonta marginata varicosa, 
collected Aug. 18, 1908; of Symphynota viridis, collected Sept. 6, 1909; of Symphy- 
nota costata, collected Aug. 31, 1906, and Sept. 21, 1907; of Symphynota complanata, 
collected Sept. 14, 1909; and of Strophitus edentulus, collected Aug. 24, 1909. All 
had no hooks, and we see that they all were collected in the months of August 
and September, the beginning of the breeding season. In other specimens of the 
identical species, collected generally a littler later in the season or in the spring, 
hooks (spines) were present. 
Thus we have every reason to believe that Sterki’s opinion that this kind of 
glochidium is common to, and characteristic of, the genera Strophitus, Alasmidonta, 
and Anodonta, is essentially correct, and that it should be enlarged so as to embrace 
all forms belonging to the ‘‘Anodonta-group.” 
A second type of glochidium presents a somewhat rectangular shape, more or 
less dilated ventrally (celt-shaped), with two spines or hooks, one at each of the 
ventral corners of the shell; further the lateral (anterior and posterior) margins 
of this shell are here not in contact all along their edges, as usual, but are gaping. 
In Pennsylvanian species, I have only observed this type in Lampsilis alata (Say) 
(See Pl. LX XXIX, fig. 18), and in addition in L. lavissima (Lea), from Kansas. 
Lea describes it (Observ. X and XIII) from the same species and from L. purpurata 
(Lamarck). 
These species stand in Simpson’s system in the subgenus Proptera of Lampsilis. 
This has induced Sterki to believe that this shape of glochidium is common. to all 
forms belonging to Proplera, and to elevate it, on that account, to generic rank. 
Although I agree with Sterki in making Proptera a genus by itself, I would 
not place all species listed under Simpson’s subgenus into it, for we have at least 
one species, which has a glochidium of a different shape. This is Lampsilis (Prop- 
tera) gracilis (Barnes) (See Pl. LXXXIX, fig. 19). Here the glochidia are in 
shape similar to those of the third type, to be described presently, but they differ 
considerably from them in size, for they are much smaller. In fact, the glochidia 
of this species are by far the smallest I know among our Unionide. The natural 
consequence is that we are compelled to create a new genus (Paraptera) for it. 
In the shape of the glochidia Lampsilis alata (and the forms allied to it) 
