1906.] NATURAL SCIENCES OF PHILADELPHIA. 237 



cephalic plate, ending abruptly behind; anteriorly it widens slightly 

 and passes partly into the marginal rim, partly into the palpode. On 

 each side of the ridge are deep sensory slits which anteriorly bend 

 somewhat sharply outward and backward, and continue along the base 

 of the lateral fold nearly as far as the posterior end of the median limb. 



From near the posterior end of the median ridge to the lateral fold 

 or notch in the marginal membrane passes a strictly transverse furrow 

 on each side, leaving an extensive area in the posterior region of the 

 head marked onl}^ by a few crescentic furrows parallel with the pos- 

 terior margin. The palpode is a short, broadly rounded, rather thick, 

 tongue-like structure which is continued backward on the ventral side 

 as a broad welt to the mouth, within which it bifurcates to form a pair of 

 ridges separated by a deep cleft. The mouth is relatively small and 

 bounded by a nearly circular fold, elevated and furrowed somewhat 

 like a piece' of rope and which is open only anteriorly to admit the 

 posterior extension of the palpode. 



As before mentioned there is absolutely no visible line of separation 

 between prostomium and peristomium, but the two together constitute 

 a continuous head, shaped somewhat like a horse's hoof; that is, it 

 spreads anteriorly, where it is truncated obliquely by the cephalic 

 plate. The seven somites next following are cylindrical, with a nearly 

 uniform diameter about equalling the posterior diameter of the 

 peristomium, and a length but little greater. All have traces of anterior 

 collars, which are best developed on IV to ^^II, on which also the 

 glandular layer of the skin is thick and extensive. The skin of the 

 head and somites II to I\' is very smooth, iridescent and marked by 

 fine furrows crossing in various directions, like those on the human 

 skin. Somites V to ^TII are of a dull, opaque, non-iridescent white. 

 Following this the body is distinctly depressed and the segments 

 elongated to two or three times their diameter. They bear prominent 

 tori situated along broad elevated longitudinal muscle bands. While 

 the greater part of the surface of the segments is smooth and has a 

 conspicuous bluish iridescence, the longitudinal muscle ridges are 

 vertically furrowed and, when the segments are much contracted, 

 these furrows are extended nearly around the segment. With the 

 exception of -^, the segments bounding which are continuous and 

 the place of transition of the parapodia from an anterior to a 

 posterior position, all of the furrows are well developed. Somite IX 

 is the last exhibiting a distinct glandular region, which is confined to a 

 narrow anterior zone. For nearly the entire length of the worm there 

 appears in the median ventral line a neural cleft in the muscles, having 



