262 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 53. 



plate bifurcated into two points, with two minute denticulations on 

 each side." From this description the lower jaw may be regarded as 

 a six-toothed jaw, having two large apical teeth and two small 

 teeth on each side. The upper jaw is not so easily understood. 

 The upper jaw bears "a?" teeth, if x=l plus y, in which statement 

 "y" is more than two {several Tninute denticulations, according to 

 Leidy). This interpretation of the upper jaw would give it a mini- 

 mum of seven teeth ; that is, one large tooth plus at least three teeth 

 on each side. 



Moore ^ figures a specimen which he assigns to Leidy's species, 

 having jaws of the dental formula 7-10. The upper jaw as figured 

 has one large apical tooth, and three small denticles on each side, and 

 the lower jaw has two large teeth, and four small denticles on each 

 side. Moore's figure of the head of this worm shows the upper lip 

 to be composed of four distinct but small lobes, and the lower lip of 

 two large subequal lobes. At the junction of the upper and lower 

 lips on each side is a small intermediate lobe. These six lobes are 

 small enough to fall in Leidy's description of a " circular or ellip- 

 tical, crenated lip." 



From the examination of a large series of specimens and a study 

 of many living individuals at Douglas Lake, Michigan, the usual 

 dental formula of this species seems to be 5-4. The upper jaw has 

 one large tooth with two small denticles on each side and the lower 

 two large teeth with two small denticles. The variation in the 

 number of teeth figured and described may be accounted for by the 

 fact that the sides of both upper and lower jaws of this species often 

 bear small tubercles below the small denticles — that is, toward the 

 base of the jaw — and these small tubercles could easily be confused 

 with teeth. As understood in this paper, a tooth or denticle is a 

 tubercle on the dental face bearing a distinct tooth cap. These tooth 

 caps are lighter in color than the dental ridge, have 5 definite points 

 and definite form. Two specimens from Tilhance Creek, West Vir- 

 ginia, one from Indian Creek, West Virginia, and one from Douglas 

 Lake, Michigan, had jaws with more teeth — that is, definite teeth 

 with tooth caps — than the regular 5-4 type, showing that some 

 variation does occur. 



The plurilobate condition of the prostomium is regular and defi- 

 nite, the upper lip having four subequal lobes, the lower, two large, 

 subequal lobes with a small, often inconspicuous, lobe present at 

 the junction of the upper and lower lip on each side of the mouth. 

 In the living worms it was observed that the four lobes of the upper 

 lip and, to a less extent, the two lobes of the lower lip could be ex- 

 tended to form distinct tentacles on the lips. Several specimens from 



»Proc. Acad. Nat. Sci. Phila. 1893, pi. 12. 



