Ortmann: Families and Genera qf Najades. '_".)•"> 



with .1 faint sculpture upon the posterior slope. Beak-sculpture 

 heavj .uid coarse, the later bars are often very thick and swollen, 

 concentric, often angled behind, not double-looped. Hinge with 

 teeth, pseudocardinals always present, laterals present or absent; in 

 the former case sometimes abnormally developed. 



Only the outer gills are marsupial, when charged, distending at 

 edges, secondary water-tubes present, and ovisacs not subdivided. 

 No placenta developed. Inner lamina of inner gills free from ab- 

 dominal sac, or more or less connected with it. Mantle-connection 

 between anal and supra-anal not very long. 



Type A. undulata (Say). 



This genus is rather primitive, especially in the character of the shell, 

 and stands on about the same level as Symphynota, representing an- 

 other parallel branch, characterized by the heavy, concentric beak- 

 sculpture. The tendency to a union of the inner lamina of the inner 

 gills with the abdominal sac indicates a slight advance in structure. 



Alasmidonta heterodon (Lea). 



About thirty specimens collected in April near Philadelphia have 

 been investigated. Among them were many gravid females. Conner 

 (1909, p. 112) found this species gravid in February. 



An imperfect description of the marsupium and the glochidia has 

 been given by Lea (Obs., X, 1863, p. 442). 



The soft parts do not offer anything remarkable. The mantle- 

 connection between anal and supra-anal is shorter than the anal. 

 Anal with crenulated inner edge. Inner lamina of inner gills free. 

 Posterior margins of palpi connected for about one-half of their length. 

 The anterior end of the inner gill is separated from the palpi, but nearer 

 to them than to the anterior end of the outer gill. Marsupium 

 typically anodontine in structure. Glochidia (Ortmann, \o\\b, 

 pi. 89, fig. 8) the smallest known to me in this subfamily. They are 

 subtriangular, much longer than high, with strong hooks. Length 

 0.30; height 0.25 mm. 



Color of soft parts whitish; charged marsupium brown. 



This is in every respect the most primitive type known to me in this 

 subfamily. 



Alasmidonta minor (Lea). 



One male, and one gravid female (with glochidia), from Cumberland 

 River, Pineville, Bell Co., Kentucky, have been communicated to me 

 b\ B. Walker. 



