Occasional Papers of the Museum of Zoology 41 



stood by Simpson. Str. undulatus is 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. 

 ('22) as a synonym. 



An examination of Swainson's description and figures leaves 

 no doubt that his species ib 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. undulatus Say. 



Genus Ptychobranchus Simpson, 1900 



Ptychobraiichus Simpson, '00*, p. 79 (type, phaseolus Barnes). 

 Ellipsaria Raf., Frierson, 'I4^ p. 7 (type, fasciolaris Raf.). 



One of the four species listed by Rafinesque under his sub- 

 genus Ellipsaria is OhUquaria ellipsariu,, and therefore, by the 

 rule of absolute tautonomy (Code, Art. 3od), it ipso facto 

 l)ecomes the type of the subgenus. O. ellipsaria is a synonym 



