Ortmann: Families \\i> Genera oi Najades. 281 



charged their edges distending, lateral (secondarj I water-tubes present, 

 ovisacs not subdivided. Placentae very poorl} developed, and only 

 indicated when eggsare present. Inner lamina of inner gills free from 

 abdominal sac. 



I\|ic S. compressa Lea. Very close to this stands 5. viridis (Con- 

 rad). These two species arc normally liermaphrodites, while the other 

 two {S. complanata (Barnes) and 5. costata (Rafinesque)) are gono- 

 chorists. 



This genus is the most primitive among the A nodontina with dnuble- 

 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 Laker, 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 papillae; 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. 



( .ills with well-developed septa and water-tubes. This species being 

 normally hermaphroditic (see Ortmann, 191 lb, 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 



