244 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 55. 



Type-species. — Xironodrilus formosus, new species. 



This genus as here defined includes two species which may be dis- 

 tinguished by the following key. 



a\ IMiddle tooth of the upper jaw the longest tooth on the jaw if the teeth are 

 odd in nnmber; middle pnir of teeth of the upper jaw subequal and longer 

 than the other teeth, if the teeth are even in number ; teeth increasmg 

 rather regularly in size from the outer edges of the jaw to the middle of 

 the jaw ; dental formula 5-4, varying from 4-3 to 6-5. X. formosus, new 

 species. 



a'. Middle tooth of the upper jaw distinctly shorter than either of the two teeth 

 adjoining the middle tooth; dental formula 4-4 or 5-4, varying from 3-3 

 to 5-5. X. pvlcherrimus (Moore). 



XIRONODRILUS FORMOSUS, new species. 

 Plate 11, fig. 2. 



Type.— Cat. No. 17626, U.S.N.M., body length 2.7 mm., White 

 River, Irondale, near Anderson, Indiana, August, 1915 (M. M. Ellis), 

 on Cambarus rusticus Girard (det. Faxon). 



Faratypes.—T&[i, Cat. No. 17627, U.S.N.M., and 10 others, col- 

 lected with the type. 



Additional specimens. — 500, White River, Irondale, near Anderson, 

 Indiana, summers of 1914-16 (M. M. Ellis), on Camharus rusticus 

 Girard (det. Faxon) ; six, one=Cat. No. 17628, U.S.N.M., White 

 River, Noblesville, Indiana, June 23, 1915 (M. M. Ellis), on Cam- 

 harus rusticus Girard ; three. Lake Michigan, Charlevoix, Michigan, 

 August 12, 1914 (M. M. Ellis), on Camharus propinquus Girard 

 (det. Faxon) ; three, Wabash River, Vincennes, Indiana, August, 

 1913 (M. M. Ellis), on Camharus propinquus Girard; one, between 

 Paoli and Wyandotte, Indiana (O. P. Hay), on Camharus rmticus 

 Girard, Cat. No. 17629, U.S.N.M. 



Description. — Body rather elongate and distinctly depressed; 

 width of the head approximately equal to that of segment I and less 

 than that of segment II; body segments increasing in width regu- 

 larly from segment I to segment VII ; segment VII usually the widest 

 segment of the body (in strongly contracted specimens and in speci- 

 mens in which segment VII is not distended with sex cells, segments 

 VII and VIII are usually about the same width, or segment VIII 

 may be slightly wider than segment VII) ; nine body segments dis- 

 tinct and easily seen in the dorsal view; each segment slightly con- 

 stricted anteriorly and posteriorly so that the junctions of the seg- 

 ments are evident; segments narrowing regularly and rapidly from 

 the middle of segment VIII to the caudal sucker ; diameter of caudal 

 sucker less than or barely equal to the width of the head ; head sub- 

 cylindrical, its anterior third defined by a groove or constriction ; lips 

 two, the upper slightly longer than the lower ; both upper and lower 

 lips with small but rather definite median emargination, otherwise 



