300 MEMOIRS OF THE CARNEGIE MUSEUM 
I have seen the identical condition in Anodontoides and Symphynota, with young . 
eggs at the base of the gills, glochidia near the edge, and with the intermediate 
stages in the middle. 
The shape of the glochidium has been studied repeatedly by different writers, 
but the credit of using it successfully for the systematic arrangement of the genera 
belongs to Sterki. The glochidium of Anodonta possibly is best known. It is 
rather large, subtriangular, with a spine at the tip of each valve (Pl. LXXXIX, 
fig. 13). Yet this shape cannot be regarded as typical, and it represents a specializa- 
tion. As Sterki points out, it is found only in that group of genera, which I have 
repeatedly called the Anodonta-group, and it is one of the diagnostic features of 
this group. 
I have seen this glochidium in the following forms: Strophitus edentulus 
(Say); -Anodonta grandis Say; A. imbecillis Say (Pl. LXXXIX, fig. 13); 
Anodontoides ferussacianus (Lea) (Pl. LXXXIX, fig. 12); Symphynota compressa 
Lea (Pl. LXXXIX, fig. 10); S. viridis (Conrad); S. costata (Rafinesque); S. 
complanata (Barnes) (Pl. LX XXIX, fig. 11); Alasmidonta undulata (Say) (Pl. 
LXXXIX, fig. 9); A. marginata (Say); A. marginata varicosa (Lamarck); A. 
heterodon (Lea) (Pl. LX XXIX, fig. 8). 
In all these the glochidia are rather uniform in size as well as in shape. Gen- 
erally they are rather high and pointed, but sometimes (Symphynota compressa 
and viridis) they are wider and less pointed. We do not need to go into detail 
here, since most of them have been already figured by Lea (Observ. VI and XIII).’ 
The glochidia of Alasmidonta undulata and Anodontoides ferussacianus are here 
figured for the first time (Pl. LX X XIX, figs. 9 and 12). 
Lea, who is the only writer, who has furnished drawings of the glochidia, 
has observed the same type in the following additional species: Margaritana del- 
toidea (= Alasmidonta calceola) (See Observ. VI); Margaritana spillmanni (= Stro- 
phitus spillmanni) (See Observ. XIII). They also belong to the same group. On 
the other hand, Lea says of Margaritana triangulata (= Alasmidonta triangulata) 
(See Observ. VI) from Georgia, that he could not observe any hooks, and the same 
is the case in Margaritana hildrethiana (= Hemilastena ambigua, see Observ. V1), 
Anodonta ferussaciana (= Anodontoides ferussaciana ibid.), and in Anodonta ovata 
(= grandis, see Observ. X). All these species should have hooks, if Sterki’s theory, 
that this is a fundamental character of the glochidia of this group, is correct. 
7A number of Lea’s figures are rather unsatisfactory, because they are not drawn to scale. Thus, for instance, the 
glochidium of Plagiola secuwris (Obsery. VI, pl. 5, fig. 6) does not show its real character, being too small in comparison with 
those of other species (also the gaping margins are not shown). The glochidia on our Plate LX X XIX are all from photographs 
taken under the same enlargement, and thus show the actual comparative proportions. 
