394 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.46. 



middle; tlie fulcrum is large, its lower end broadly fan-shaped and in 

 the transverse plane, so far as known the only instance of its kind. 

 The rami consist of a network of ribs, roughly semicyhndrical in shape; 

 each ramus is pierced by two large holes. A rod-shaped epipharynx 

 with decurved ends assists in supporting the oral region. 



Total length 130 a; trophi, 42 /x. 



Type.— Cat. No. 16516, U.S.N.M., was collected at Kenilworth, 

 District of Columbia, where the species occurs in fair numbers among 

 the weeds in shallow ponds throughout the greater part of the year. 



That this species belongs to the Notommatidse is evident; the corona 

 is of a frequently recurring type and not far removed from that of the 

 genus Diascfiiza. The frontal papillae, while very characteristic, are 

 probably of small systematic importance, as they are found in widely 

 varying degrees of development in otherwise closely related species. 

 The mastax is, however, of such an unusual type, that it seems ad- 

 visable to make this species the type of a new genus. It has been 

 named for Mr. Charles F. Rousselet, of London, to whom every 

 student of the Rotatoria, including the writer, is indebted for generous 

 assistance and advice. 



ENCENTRUM APER, new species. 

 Plate 34, figs. 7-10. 



The body is slender and nearly cyUndric, passing rather abruptly 

 into a short foot. While the integument is very flexible and without 

 any indication of any segmentation when the animal swims, some 

 inconspicuous transverse folds appear when it is crawhng about in 

 search of food. One fold is immediately behind the auricles, a second 

 separates the head from the body, and a thii"d marks off a short pos- 

 terior segment. The foot is short and considerably smaller than the 

 last segment of the body; the anterior portion of the toes tapers 

 gradually to a fine, shghtly decurved point. 



The corona is almost ventral; the auricles are not veiy prominent. 

 At the base of the moderate-sized anterior hook or ligula, in front of 

 the auricles, there is on each side a sUght emargination for the insertion 

 of a ''tusk," or tooth-hke projection. The purpose of tliis structure 

 is unknown; nothing similar is to be found among the related species 

 available for comparison. It is not a mere flap of the integument, 

 but a well-defined, bluntly conical tooth of high refractive index, 

 which demonstrates its abrupt termination at the point of msertion; 

 there is no suggestion of a gradual transition to the normal structure 

 of the integument. Immediately behind this "tusk" a tuft of veiy 

 long and stout, immobile sensory setae project laterally and somewhat 

 posteriorly. 



The ganghon is large; a small retrocerebral sac is present, but no 

 subcerebral glands. While no eyespots are visible in the living or 



