Occasional Papers of the Museum of Zoology 41 
stood by Simpson. Str. undulatus 1s a smaller shell, with 
more inflated and prominent beaks, and more tapering poste- 
rior end. It is positively known only from the tidewaters 
(Delaware and Schuylkill rivers) near Philadelphia. 
Walker calls attention to the mistake made by Simpson in 
retaining edentulus Say (’29), although he gives rugosus Sw. 
(722) as a synonym. 
An examination of Swainson’s description and figures leaves 
no doubt that his species is the inflated, black form of S. 
edentulus that occurs in the eastern states and is usually sent 
out as S. undulatus Say. 
Swainson’s description is as follows: 
“Shell transverse, oval; rather thick and ventricose; both 
extremities obtuse; the anterior side (from the umbones to 
the exterior margin) obliquely rounded; umbones prominent ; 
hinge margin rather thick, slightly curved and swelled imme- 
diately under the umbones; sinus short, abrupt, curved; epi- 
dermis coarse, black and much wrinkled; inside stained with - 
yellow and having a narrow reddish rim or margin.” 
-_ 
No dimensions are given, but the figures (3) measure: 
length 63, height 39, diameter 32 mm. 
No exact locality is given, but it is stated that the specimens 
came from the United States. 
This is quite different from the typical S. wndulatus Say. 
Genus PryCHOBRANCHUS Simpson, 1900 
Ptychobranchus Simpson, ’00*, p. 79 (type, phaseolus Barnes). 
Ellipsaria Raf., Frierson, ’14°, p. 7 (type, fasciolaris Raf.). 
One of the four species listed by Rafinesque under his sub- 
genus Ellipsaria is Obliquaria ellipsaria, and therefore, by the 
rule of absolute tautonomy (Code, Art. 30d), it ipso facto 
becomes the type of the subgenus. O. ellipsaria is a synonym 
