1909.] NATURAL SCIENCES OF PHILADELPHIA. 271 



behind which is the broad, tumid crescentic tentacular ridge, bearing 

 the very numerous tentacles in about eight transverse rows. 



Peristomium very short and obscure dorsally; ventrally prolonged 

 into a prominent scoop-like fold bearing a tumid lower lip and 

 produced laterally into a pair of rather prominent, broadly rounded 

 wings. Next three segments short, somewhat depressed, and branch- 

 iferous. A pair of prominent, rounded, lateral wings arise at a level 

 somewhat more dorsal than those on the peristomium and conceal 

 the greater part of the sides of II. Remaining thoracic somites are 

 much longer and subterete, 3 or 4 annulate, with prominent, glandular 

 parapodial areas and the dorsal and ventral fields much transversely 

 wrinkled. Ventral gland plates on II to XIII inclusive, but all rather 

 inconspicuous and the first especially small. Abdominal segments 

 very numerous, flattened and muscular below, arched and thin-walled 

 above. Pygidium annular with a brownish thickened rim bearing 

 a circle of about sixteen small, equal papillae surrounding the large 

 anus. 



Gills three pairs, on II, III and IV; except in one case all present 

 and well developed, symmetrical, usually decreasing in size from before 

 caudad, those of the middle pair arising at a slightly lower level than 

 the others. Owing to their great contractility they differ much 

 in form and appearance, but are strictly aborescent and more or less 

 open according to the degree of contraction. When fully extended 

 the stem is a smooth, tapering column having a length equaling or 

 exceeding the thoracic diameter and bearing at the summit four or 

 five main branches, each of which again divides about six times and 

 terminates in slender tapered filaments. The plan of division is 

 dichotomous but irregularities are numerous, and although the trunk 

 cannot be traced through the crown, one branch of a pair is usually 

 larger than the other and frequently a single long tapering filament 

 occurs opposite the point of origin of a branch of any order. When 

 contracted the branches appear short and cylindrical, with the fila- 

 ments in crowded terminal tufts. The latter are readily detached and 

 regenerated. 



Setigerous tubercles begin on IV and continue for seventeen seg- 

 ments or to XX. They are large, prominent, well separated from 

 the tori, somewhat flattened and bear broad fascicles of seta?. The 

 first pair (on IV) are smaller, and small papilliform cirri occur behind 

 the setigerous tubercles of VI to X inclusive. Uncinigerous tori 

 well marked and regular, retractile ridges separated from the setiger- 

 ous tubercles by an interval exceeding the diameter of the latter. 



