ORTMANN: monograph of the naiades of PENNSYLVANIA. 195 



Genus Strophitus Rafinesque (1820). 

 Ortmann, 1912, p. 299; Simpson, 1914, p. 344. 



Type Anodonta undulata Say. 



Two species of this genus are generally credited to Pennsylvania, but I have 

 been able to find only one {S. edentulus), which is distributed all over the state 

 both on the western and the eastern side of the mountains. The type-species 

 possibly originally came from Pennsj'lvania, but being founded upon a very poor 

 and immature specimen, has been largely misunderstood. Simpson (1900, p. 618; 

 1914, p. 345 & 349) admits the existence, on the Atlantic side, of "a small, thin 

 form, . . . usually biangulate behind," but I have not been able to locate it. 



Conner believes, that he has rediscovered the true S. undtdatus of Say, and I 

 have received from him specimens from the New Jersey side of the Delaware River 

 (not far from the supposed type-locality of Say's specimen, on the Pennsylvania 

 side of the river). However, I can see only a local race of the common S. edentulus 

 in this, probably belonging to the tidewater region of the Delaware River, and 

 connected by intergrades with the common form, wherever the latter goes into 

 large and more quiet bodies of water. But since my material is entirely insufficient 

 to solve the question, I shall mention here the two forms as species, thus avoiding 

 the inconvenience of having to call the typical, common form by a varietal name 

 {S. undulatus edentulus), and making the local race the main species (*S. undulatus). 



Strophitus undulatus (Say) (1817).^^^ 

 Simpson, 1914, p. 349 (but synonymy largely incorrect). 



Plate XII, fig. 6. 

 Records from Pennsylvania: 



Say does not give a type-locality for his Anodonta undulata, but his specimen probably came from 

 near Philadelphia. 



Lea (Obs. II, 1838, p. 54, and Obs. X, 1863, p. 450) repeatedly reports A. undulata Say from the 

 Schuylkill River, near Philadelphia, and distinguishes it from A . edentula. The mouth of the Schuylkill, 

 on the Delaware is just opposite the locality where Conner obtained liis specimens. 



All other records for this species are either very doubtful, whether they belong to the true undu- 

 latus, or are positively referable to S. edentulus. 



(See Ortmann, 19096, pp. 194 & 205.) 



Characters of the species: Like S. edentulus in every particular, except that the 

 beaks are slightly more inflated, elevated, and incurved. In consequence of this 

 the shell appears higher anteriorlj', and more tapering and pointed posteriorly. 



"6 Not 1816. 



