1906.] NATURAL SCIENCES OF PHILADELPHIA. 235 



tori. Somites IX and X are indistinguishable, and on the latter the 

 now prominent tori have shifted to the posterior end of the segment. 



From this point the segments continue to lengthen to XIV, which is 

 about three times as long as thick, after which they again decrease. 

 Throughout the middle region the integuments are soft and translucent, 

 except for the swollen, oval, glandular areas surrounding each torus. 

 Somites XVIII, XIX and XX are again much thicker than long 

 and the tori are correspondingly large and prominent; XX is al^out 

 one-fourth as long as thick with a prominent pair of achaetous tori 

 much below the usual level and meeting ventrally. 



The pygidium consists of a very short basal ring bearing a pair of 

 coalesced glandular thickenings corresponding to the tori of XX. 

 The anus is conspicuous and in a dorsal position at the base of the 

 dorsal membrane. The limbate margin of the pygidium bears a re- 

 markable reseml^lance to the cephalic plate, but is oblique in a reverse 

 ■direction. Its ventral two-fifths are separated rom the dorsal three- 

 fifths by a deep rounded notch, with thickened margins which nearly 

 meet externally and constrict its opening. The ventral portion has its 

 margin marked by four very broad, shallow crenulations and a pair 

 of prominent triangular lateral lobes. The dorsal plate is more 

 prominent and flaring, with a smooth and regular margin marked 

 only by a broad and extremely shallow median emargination. 



Somites I and II and the pygidium are achsetous; II bears strictly 

 lateral setaj only, arranged in a vertical tuft just above the dorsal ends 

 of the ventral collar; III and IV bear similar setse tufts and very short 

 series of uncini disposed in the same plane and both strictly lateral 

 and sessile. On succeeding segments the setae tufts have short, slightly 

 oblique bases placed a little in advance of the uncini, which form lines 

 five or six times as long as those on the preceding somites, more ventral 

 in position, and elevated upon distinct tori. Proceeding caudad the 

 uncinial lines increase slightly in length and become more ventral in 

 position. The number of uncini in a torus is about 8 on III, 13 on V, 

 28 on X, 32 on XV and 35 on XIX. 



The small tuft on II contains setse of two kinds, the one small with 

 a rather wide wing and abruptly tapered stem terminating in a slender 

 tip ; the other very much longer, with the stem conspicuously striated 

 the tips rigid and less slender and the wing very narrow (fig. 26). 

 On follomng somites the number of setse increases to 10 or 12 pairs, 

 the larger ones become stouter and the smaller more slender. By 

 somite XV the number is further reduced ; the small setse exhibit only 

 minute pointed tips and the ends of the larger ones are elongated and 



