1903.] NATURAL SCIENCES OF PHILADELPHIA. 407 



On the cirri-bearing somites are smaller, and structurally somewhat 

 simpler, but essentially similar structures, through which transverse 

 muscles pass into the parapodia and dorsal cirri. As will be indicated 

 below, they bear branchial filaments similarly to the ely trophores, with 

 which they are obviously homologous. 



Branchial filaments occur on every somite from III to XXIV inclu- 

 sive, except XXIII, the last somite bearing elytra, and minute rudi- 

 ments on the anterior side even of XXV and XXVI. They appear 

 to be mere hollow integumental sacs generally of simple finger-hke form. 

 On elytra-bearing somites they are disposed as follows : One arises from 

 the antero-external and one from the postero-external margin of the 

 elytrophore. The former is present on every elytrophore except 

 the first antl last, is unbranched but bends sharpl}^ laterad at a 

 right angle. The latter is longer, and on typical somites divides 

 into a short medial and a long lateral branch diverging at right 

 angles from the short stem ; it is altogether absent on the first and the 

 medial branch is wanting on the 11th and a few of the anterior 

 ely trophores. On the parapodium are 2 dorsal, 5 or 6 anterior and 

 4 or 5 posterior filaments (in addition to 1 or 2 rudimentary ones on 

 the base of the ely trophores), the most ectal one in each case being 

 bifid. Anterior to the 5th and posterior to the 11th elytra-bearing 

 somite this arrangement is simplified by reduction in the number of 

 filaments. Essentially the same arrangement obtains on the cirri- 

 bearing somites, but the filaments are more numerous, larger and 

 sometimes even trifid. The elytrophore filaments are represented 

 anteriorly by 2 simple ones, and posteriorly by 3, of which the middle 

 one is bifid. There are usually 5 dorsal parapodial filaments, of which 

 one at the base of the cirrus, like the most external on the anterior 

 and' posterior faces of the parapodia, is usually trifid. 



The parapodia are stout, with the neuropodium of a somewhat com- 

 pressed, obliriuely truncated conical form and the notopodium a rather 

 prominent short tubercle on the anterior dorsal face near the base of 

 the parapodium. The ventral surface of the parapodia, and indeed 

 of the entire body, is covered with a close nap of short, fine processes. 

 Ventral cirri with low tubercle-like ceratophores borne on the middle 

 of the ventral neuropodial surface; their styles short, scarcely reaching 

 half-way to the end of the foot, the basal half stout and swollen, the 

 distal tapered to a sharp point, but with no proper filament. The 

 dorsal cirri are quite long, their filamentous tips at least reaching quite 

 beyond the setse line; they have exactly the shape and color of the 

 tentacular cirri, but on the base of each is a prominent bilobed glandu- 



