264 bulletin: museum of comparative zoology. 



usual. Neuropodial crochets begin on or near segment XXV. Total number 

 of segments in type one hundred and fifty-five. 



Length 58 mm.; width 5 mm. 

 Locality. — Panama. 

 Type — M. C. Z. 1,285. 



Terebellidae. 



28. PiSTA BREVIBRANCHIA, Sp. nOV. 



Plate 2, fig. 1-4. 



This species much resembles P. fratrella Chamberlin, known from Laguna 

 Beach, Cal., which it approaches in form of the uncini of the several regions 

 more closely than it does P. alata Moore. It differs from both these species 

 in having much smaller branchiae with fewer branches and much shorter 

 trunks. There are two pairs, arising on II and III respectively. Of these 

 the posterior much exceed the anterior in size, with the right posterior largest. 

 The anterior branchiae with terminal branches very short, the entire organ in 

 length scarcely equalling that of the trunk of the right posterior. Branchiae 

 of each pair attached close together, trunks nearly contiguous at middle line. 

 Tentacles in a transverse series, attached by contracted bases; short and rather 

 thick but distally moderately tapered. On tentaculiferous ridge above and 

 on anterior surface of peristomial collar-lobes above numerous short papillae. 

 Peristomium with anterior edge produced into a prominent flaring collar with 

 ends widely separated above; deeply emarginate ventrally, leaving the lateral 

 portions as prominent wings. Second somite with .anterior edge produced 

 across ventral surface and part way up each side, the wing laterally over- 

 lapped on each side by the larger one of III. The latter is scarcely evident, 

 obsolete, across venter, but forms a very prominent wing on each side which 

 rises to a level in front of the setigerous tubercle of IV and thus considerably 

 farther dorsad and mesad than the peristomial collar; the wings are not 

 united across the dorsum, the dorsal surface of III simply depressed below the 

 level of IV. Along the anterior edge of IV on each side also a well-developed 

 wing which, however, is much lower than that of III and does not extend so 

 far dorsad. On V and VI are similar but smaller wings which do not extend 

 half way to the setigerous papillae, and a smaller one on each side of VII. 

 The thoracic setae are distally moderately curved with the limbus on the con- 

 vex side broad, the other one narrow. As in fratrella the uncini show pro- 

 gressively reduced manubria in the anterior double rows as well as in the 

 single rows farther forward. In these there is a distinct rounded shoulder 

 besides at the base of the manubrium on the side toward the neck of the plate. 



