ODONTOSYLLIS ATYPICA. 181 



The proboscis presents the usual thickening, with the series of recurved teeth. 



The peristomium is reduced and concealed above, but is distinct laterally 

 and below. It is achaetous and bears two pairs of tentacular cirri. Of these 

 the ventral are clearly the shorter; the dorsal ones are subequal to or but little 

 longer than the tentacles. They are strongly jointed. The nuchal organ is 

 in the form of the characteristic flap, appearing distinctly to arise from the 

 dorsum of somite II and extending forwards over the median part of the pro- 

 stomium to a point caudad of the level of the middle of the posterior eyes. It 

 is broadly subtriangular and distally widely rounded and with the lateral edges 

 curving evenly out ectad at the base. The second and succeeding somites are 

 setigerous. All are simple and very short, smooth. Pygidium not observed. 



The parapodia of the anterior region are uniramous. They are short and 

 conical with the distal end obliquely truncate, the ventral edge being shorter 

 than the dorsal, the composite setae, which are alone present, arising from a 

 furrow along the truncate surface. The neurocirrus in each arises on the ventral 

 surface near the proximal end of the oblique surface; it is a stout, short, conical, 

 and translucent process not exceeding the end of the neuropodium, and without 

 annulations. The notocirri arise on the dorsal surface at the very base from 

 stout and rounded eminences in diameter greatly exceeding the style, which is 

 slender; the style extends well beyond the setae; it is strongly jointed. The 

 cirrus of the second somite is much longer than the other cirri and than the 

 tentacular cirri, extending back to about the fourteenth somite. The notocirrus 

 of the third somite is short, of nearly normal length, while that of the fourth 

 and even more so that of the fifth is much more elongate, that of the parapodia 

 of the sixth somite shorter and of the length typical for remaining region of the 

 body. The parapodia of the middle region are biramous, a short conical noto- 

 podium appearing above at the base of the foot and bearing a fascicle of long 

 simple setae. The composite setae and the cirri have the same general character 

 as those of the anterior region. In the posterior region the parapodia are again 

 uniramous, the notopodium being absent. (Plate 21, fig. 4). 



Acicula of the neuropodia typically two in number, stout, Ijdng in close 

 contact with each other. The notopodial aciculum single, more slender than 

 the neuropodials, distally gently curved. The neuropodial, or composite, setae 

 are all subacicular in position and are arranged in several series. The shaft is 

 distinctly curved; it enlarges clavately distad, more abruptly at the very end 

 about the socket; the distal edge is oblique and appears smooth, but is really 

 obscurely dentate, with the apical tooth largest. The terminal appendage is 



