1904.] NATURAL SCIENCES OF PHILADELPHIA. 497 



tion distinctly reflexed. Eyes absent. Tentacles very numerous, 

 deeply grooved, arising from the posterior border of the prostomium 

 for its entire width in three or four transverse crowded rows, behind 

 which is a slightly elevated border. Most of the tentacles are colorless, 

 but usually some are pale brown. Mouth large with a broad peris- 

 tomial lower lip. Peristomium about as long as succeeding somites, 

 distinctly visible as a ring both above and below. 



Branchise two pairs on the posterior part of somites II and III, the 

 first just anterior to the first seta3 tuft, the second above and behind it. 

 All of the branchise are prominent, and of about equal size. They 

 are of a spreading bushy form; the main stem very short, dichotomy 

 occurring almost immediately and the outermost branch again dividing 

 at once, so that three main branches appear to arise almost separately. 

 After about four or five dichotomous divisions, which are usually un- 

 equal, one or two uregular divisions occur, the result being a very 

 large number of terminal twigs. When contracted the minor divisions 

 coil inward toward the axis, so that the gill presents a very compact 

 appearance. There is, however, much irregularity in this respect, 

 some of the filaments merely shortening, others coiling spirally. 



The body is slender and club-shaped, nearly terete throughout the 

 abdominal region, gently tapered to the anus and the anterior end of 

 the thorax somewhat enlarged. The thoracic segments increase 

 slightly in diameter to about X, and then decrease very gradually into 

 the abdominal region. The dorsum is regularly arched, the venter 

 somewhat angulated, fiattened or slightly convex, according to the 

 state of the specimen. Above the somites are somewhat indistinctly 

 separated and somewhat irregularly divided into three rings which are 

 usually again biannulate. On the ventral half the intersegmental fm'- 

 rows are well marked and the somites only biannulated. This region 

 is also rough and thickened, and separated from the faintly granu- 

 lated, thin-walled dorsal region by a longitudinal groove below which 

 is a ridge-like row of glandular thickenings. The first one or two ven- 

 tral plates are very short. They increase in length to the tenth, and 

 in width decrease regularly and gradually to the sixteenth, which is 

 square, while the tenth is twice, and the fifth three times as wide as 

 long. Usually a cross-furrow divides each one and the surface is 

 wrinkled. On most specimens the fifth or sixth plate is sunken below 

 the general surface. Behind the sixteenth they become very small, 

 but may be traced for some distance further. The thorax passes very 

 gradually into the abdomen, which is very prommently arched and 

 thin-walled, the somites numerously and finely ringed and indistinctly 

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