1094,] NATURAL SCIENCES OF PHILADELPHIA. 491 



specimens are 300 mm. or more in length, and have a width of 3.5 mm. 

 without and 5 mm. inckiding the parapodia. The usual number of 

 somites is about 330. The prostomium is sugar-loaf shaped in outline, 

 slightly depressed, the length slightly exceeding the basal width, the 

 apex narrowly rounded; at the base it is slightly mortised into the 

 peristomium above and on the sides is marked by a pair of faint 

 oblique grooves, in front of which are a few pigment spots but no dis- 

 tinct eyes; on the middle of the lower surface is a shallow median de- 

 pression. Mouth large, bounded laterally by a pair of prominent 

 L-shaped lobes connected with the peristomium, a much wrinkled fold 

 of which bounds the mouth posteriorly. The peristomium is divided 

 into two rings (perhaps somites) by a furrow which is very distinct 

 above, obsolete below; the first ring equals the first setigerous somite, 

 the second is two-thirds as long. Body nearly terete, very slightly 

 depressed toward the ends; the somites all well marked, simple, 

 smooth except for a very slightly raised welt around the middle ; their 

 length nearly uniform, from one-third to one-fifth their width, which 

 is greatest at the middle. Toward the posterior end of the body there 

 is a faint neural groove. The pygidium is a small platform ventral to 

 the anus and provided with a pair of prominent short and thick bifid 

 cirri, the median lobes of which come into contact in the median line. 

 In the middle region of the body the parapodia are situated about 

 midway between the dorsal and ventral surfaces which are equally con- 

 vex, but toward the ends they assume a lower level and the ventral 

 surface becomes flattened. The parapodia (PI. XXXVII, figs. 19-21) 

 have a short, thick rounded base, a very small notopodial tubercle 

 which receives four to six aciculi, a presetal lobe which is very short, 

 thick and rounded throughout the series, and a promment postsetal lobe 

 which gradually increases in size from before backward, and in the 

 middle and posterior regions has the form of a long finger-like process 

 which generally bends abruptly upward at a right angle and rises above 

 the back. The setae are of the usually acute, winged and the hooded, 

 hooked forms and vary greatly in details and particularly in the degree 

 of curvature and geniculation. The anterior parapodia contain the 

 acute type only (PI. XXXVIII, figs, 23 and 24), at first in a somewhat 

 broken fan-shaped tuft, but soon in a dorsal group of longer and 

 middle and ventral groups of shorter setae. At about XLV, guarded 

 imcini (PI, XXXVIII, fig. 25) appear in the ventral group, and by L 

 are alone present to the number of four or five, which is further reduced 

 to tw^o or even one posteriorly. The ventral setae of the dorsal bundle 

 exhibit a reduction in size at about L, and by LX have given place 



