1903.] NATURAL SCIENCES OF PHILADELPHIA. 439 



Branchiae appear and cease abruptly, occupying somites V to 

 XXXVI, caudad of which they do not ordinarily occur. Each arises 

 in common with a notopodial cirrus from a very short base, and the 

 main stem curves gently over the back to meet its fellow of the opposite 

 side at the middle line ; the stem tapers and the erect pinnae arise from 

 it separated by intervals of ^ their diameter; they are of unequal 

 length, the middle ones about equalling the notopodial cirrus, and the 

 end of the stem bends upward as the last branch. At both ends of the 

 branchial region the. number of pinnse is subject to considerable vari- 

 ation, the following figures being the average of 3 specimens upon 

 which all were counted. They appear as a small process on V which 

 elongates on VI, become trifid on VIII, and have 4-6 branches on IX, 

 7-9 on X, 12 by XIV, 14 at XVIII or XIX, which number is retained, 

 occasionally rising to 15, to about XXX or XXXII, and then falls 

 rapidly to 10, 7, 5 and none on successive somites. 



Typical parapodia bear setae of three kinds, all slender, delicate, and 

 colorless. First, compound setae: numerous, in a fasciculus on the 

 ventral part of the neuropodium ; stems curved, with a short abruptly 

 enlarged end striated axially and serrated on one margin; appendage 

 slender, elongated (most so anteriorly) , with the end weakly hooked and 

 faintly bidentate, the margin finely serrated, the guard greatly pro- 

 longed in a mucronate tip equal to ^ or more the length of the append- 

 age. Second, very slender elongated capillary setae arranged in a row 

 which extends around the dorsal and posterior sides of the fascicle 

 of compound setae; these taper gently and uniformly, and appear to 

 be nearly or quite smooth. Third, paddle-shaped pectinate setae in 

 a small fascicle just dorsad of the acicula, very delicate and terminated 

 by 9 or 10 points, of which the 2 marginal ones are somewhat unequally 

 prolonged; these are very inconspicuous, being concealed by the bases 

 of the capillary setae, i^nd the flattened ends are placed horizontally. 



The ordinary acicula are pale yellow, 2 in number, 1 much stouter, 

 simple, tapering, with bliuit slightly bent tips. 



Beginning with the mid-branchial region and continuing caudad 

 1 or 2 additional sigmoid uncinate acicula with guarded, hooked, trifid 

 tips appear on the ventral margin of the neuropodium. 



All jaws pale brown except the white calcareous mandibular plates. 

 ]\Iandibular carriers broad anteriorly, but tapering rapidly to very 

 slender divergent posterior ends, about twice the length of the calcare- 

 ous plates ; the latter somewhat triangular, the angles anterior, postero- 

 medial and postero-lateral, inclined to the earlier at an angle of about 

 45°, but the anterior angle bent forward so as to lie in a longitudinal 



