1906.] NATURAL SCIENCES OF PHILADELPHIA. 507 



region, slender and tapering behind. Length 30 mm., diameter nearly 

 2 mm. at inflated part of thorax. Number of somites 80, IV- 

 XXVIII setigerous. 



Prostomiiim broad and depressed at the base, produced forward into 

 a rather thick, simple lip, broadly romided, entire and usually curved 

 upward at the anterior margin, little folded about the mouth laterally 

 and not meeting the lower lip ; tentaculif erous ridge in contact with the 

 lateral ends of the lip but separated from it by a slight notch, arched 

 over the dorsum of the prostomium posteriorly and. bearing -in a con- 

 tinuous series about 30 coarse tentacles about one-half the length of 

 the body. No eyes visible. 



Mouth large, bounded below by a ventral lip which is divided bj^ a 

 transverse furrow into an inflated internal portion and a flat external 

 portion, which is very broad and extends laterally beyond, but does 

 not touch the upper lip. Peristomiirai a short, simple ring dorsally, 

 ■expanded ventrally to form the lower lip. Somite II as long as the 

 prostomium and ventral lip combined, its anterior margin without a 

 true collar or lateral wings, but slightly produced as a free rim. Thora- 

 cic region distinctly segmented, the furrow complete and well defined; 

 dorsal region most inflated at X-XII, thence gradually tapered to the 

 abdomen. Abdomen attenuated, nearly quadrate in section, the 

 dorsimi only rounded; the segments becoming very short but all dis- 

 tinctly biannulated, the posterior borders wider and somewhat project- 

 ing. Pygidium a simple, rugous ring. 



Ventral plates 14 (II-XV) all, except the first, sharply defined but 

 in contact with one another; the anterior ones rectangular, 2-4 times 

 .as broad as long, the last fom- elliptical and one and one-half times to 

 twice as broad as long. Posterior to the ventral plates a ventral 

 groove with a raised neural line continues to the posterior end. 



Gills (fig. 15) three pairs, on II, III and IV, decreasing in size from 

 before backwards, all small; when fully extended the first not more 

 than one-half the thoracic diameter, each with a short trunk dividing 

 near the base into 2-4 main branches, each of which then dichotomizes, 

 usually three times and terminates in slender, tapering twigs. 



Setigerous papillae begin on IV just beneath the last gill, and are 

 represented in a corresponding position on III by a minute achsetous, 

 knob-like papilla. Anteriorly they are prominent and at a high level ; 

 posteriorly they shift ventrad and become smaller. First torus on V, 

 about one-half as long as the longest on XII, and one-sixth or one- 

 seventh the body circumference. First five tori separated ventrally 

 "by about three times their length, those on XII by an interval about 



