NO. 3668 PTERODRILUS—HOLT 3 
P. distichus. Goodnight (1940, pp. 58-63) quoted the original de- 
scriptions of the four nominal species of Pterodrilus and added a new 
locality record for P. durbini. Later, he recorded the presence of P. 
aleicornus in Sinking Creek, Giles County, Va. (Goodnight, 1941b, 
p-. 468). A new species was recognized and previously known ones of 
the genus were redescribed in my unpublished dissertation (Holt, 1951, 
pp. 100-148). Later I reassigned P. durbini, placing it in the newly 
established genus Hilisodrilus (Holt, 1960b, pp. 173-176). Recently, 
P. aleicornus and its distribution have been discussed (Hobbs, Holt 
and Walton, 1967, pp. 61, 71, 73-74). Causey (1955, p. 44) recorded 
the presence of P. mexicanus in Arkansas. Other than passing refer- 
ences (e.g., Hoffman, 1963, pp. 294, 295) or mention in various keys, 
nothing else has been written about the genus Pterodrilus by North 
American authors. In Europe, however, Moszyifiski (1937, pp. 71-72; 
1938, pp. 99-103) and Georgévitch (1955, pp. 200-203; 1957, p. 14) 
described species that they had assigned to Pterodrilus, but Pop (1965, 
pp. 223-225) pointed out the obvious fact that these European species 
were based upon material belonging to the genus Branchiobdella and 
synonomized them with B. parasita Henle, 1835. They are as follows: 
Pterodrilus karamani Moszyfiski, 1937; Pterodrilus bidens Georgévitch, 
1955; Pterodrilus megas Georgévitch, 1955; Pterodrilus prion Georgé- 
vitch, 1955; Pterodrilus megodont Georgévitch, 1955; Pterodrilus 
aliata Georgévitch, 1957; Pterodrilus dantata Georgévitch, 1957. 
Pteredrilus Moore, 1895 
Typr-species.—Pterodrilus alcicornus Moore, 1895a, pp. 449-450, 
by subsequent designation (Goodnight, 1940, p. 58). 
Diacnosis.—Small branchiobdellids (known forms less than 2.0 
mm in length) of delicate appearance; cylindrical; prosomite of seg- 
ment VIII always with elevated dorsal ridge, those of other segments 
often so, dorsal ridges often bearing fan- or finger-like projections; 
jaws delicate, light in color or colorless, triangular in shape, dental 
formula 5/4; prostate present, incompletely divided from spermiducal 
gland; bursa ovoid to pyriform, penis sheath short, penis non-eversible; 
spermatheca with long ectal duct, bulb clavate or spatulate; anterior 
nephridia open by common dorsal pore on segment III. 
ArFInities.—The close relationship of the species of Pterodrilus to 
those of Cambarincola has been discussed earlier (Hoffman, 1963, pp. 
294-295), and the exclusion of the species at present assigned to 
Cambarincola from the older genus Pterodrilus has elements of arbit- 
rariness that require discussion. 
Part of the argument for maintaining the generic staus of the two 
groups of closely related species is based upon a conservative desire 
