50 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 10 



stomium, is apodous and provided on its dorsal side with a pair of cirri, 

 as in Onuphis. The first few parapodia are often larger than those follow- 

 ing and provided with hooded hooks that terminate in 2 or 3 teeth. Pec- 

 tinate (comb) setae, where present, are disposed in a close fascicle of few 

 to many, in an anterodorsal position of the neuropodium, anterior to the 

 superior limbate setae. The subacicular hooded hooks are usually yellow, 

 number 2 in a parapodium, terminate distally in a bidentate hook, first 

 make their appearance after a short anterior region, and are continued 

 posteriorly perhaps to the end or near it. Dorsal cirri are typically cirri- 

 form ; a fine embedded fascicle of notoacicula is usually present. Ventral 

 cirri are cirriform usually through 4 (to 3 or 5) segments, thereafter 

 they are low, padlike. Branchiae are usually present from the fourth or 

 fifth setiger, continued through a longer or shorter anterior and median 

 region, or totally absent in median and posterior regions. 



The proboscidial armature is much as in species of Onuphis. Man- 

 dibles consist of a pair of flattened, elongate plates, fused for a short dis- 

 tance. The maxillary parts consist of falcate forceps (maxilla I), dentate 

 plates II to V, the right plates III and IV fused to form a single piece; 

 the distal plate (V) is usually a single tooth or flat plate. 



Species of this genus are sometimes very difficult to identify with cer- 

 tainty except by examination of microscopic parts. Conspicuous features 

 such as the distribution of the great spiraled branchiae, the occurrence and 

 kind of subacicular hooks, and other characters that have sometimes been 

 used for specific definition are too uniform throughout the genus to have 

 diagnostic value. The branchial arrangement varies within the life his- 

 tory of an individual, juveniles usually having a simpler branched ar- 

 rangement and comparatively fewer branches than have older individuals ; 

 also, the branchiae may look quite dififerent with various methods of fix- 

 ation, especially if fixed within the tube or free from it. All known species 

 have subacicular hooks that are uniformly yellow, distally bidentate, al- 

 though in some there is a tendency toward a simple condition in some pos- 

 terior segments {D. obliqua, p. 57). However, since representatives of 

 this genus are usually fragments when collected, usually lacking posterior 

 ends, this character may be indeterminable. Pigmentation pattern in life, 

 though perhaps specific, is too fugitive to be of practical value. The char- 

 acter of the tube is also believed to be unique for species, but it is fre- 

 quently lacking from collections. A more satisfactory method for determi- 

 nation of species is much needed, but until greater numbers of individuals 

 of described species have been made more thoroughly known, this will be 

 difficult. 



