ORTMANN: FAMILIES AND GENERA OF NAJADES. 281 
charged their edges distending, lateral (secondary) water-tubes present, 
ovisacs not subdivided. Placentz very poorly developed, and only 
indicated when eggs are present. Inner lamina ot inner gills free from 
abdominal sac. 
Type S. compressa Lea. Very close to this stands S. viridis (Con- 
rad). These two species are normally hermaphrodites, while the other 
two (S. complanata (Barnes) and S. costata (Rafinesque)) are gono- 
chorists. 
This genus is the most primitive among the Anodontine with double- 
looped beak-sculpture. Simpson divides it into subgenera, which are 
well characterized, although there is not much need of a division of 
the genus on account of the small number of species. 
Symphynota compressa Lea. 
Numerous specimens from northwestern Pennsylvania and other 
parts have been investigated. 
This is a typical bradytictic form, and the breeding season is normal, 
beginning in August, and ending in May (and June in Lake Erie). 
The soft parts have been described by Lea (Obs., X, 1863, p. 423, 
as pressus), and Simpson (in Baker, 1898, p. 59). 
Anal and supra-anal separated by a well-developed mantle-connec- 
tion, which, however, is shorter than the anal. Inner edge of anal 
distinctly crenulated, that of the branchial with papilla; farther in 
front the edge is practically smooth, only in the beginning fine crenu- 
lations are seen. Palpi subfalciform, their posterior margins united 
for about one-half of their length. 
Gills broad, the inner the broader. Anterior end of inner gill 
about half way between the palpi and the anterior end of the outer 
gill. Gill-diaphragm normal. Inner lamina of inner gill free, except 
at anterior end. 
Gills with well-developed septa and water-tubes. This species being 
normally hermaphroditic (see Ortmann, 19110, p. 309), the gills have 
always (with extremely rare exceptions) the female structure, that is 
to say, in the inner gill the septa are rather distant, and the water- 
tubes are wide, and the outer gill is marsupial. When sterile, the 
septa are crowded, with marsupial epithelium, and the water-tubes 
are narrow. When gravid this gill swells considerably, and at the 
edge the tissue distends, so as to render the edge rounded off or trun- 
cated. Within this gill, each water-tube develops the characteristic 
