^56 PROCEEDINGS OF THE ACADEMY OF [July, 



medially and is separated by a deep, narrow incision from a similar 

 but thinner wing borne upon the base of the dorsalmost branchial stem. 

 Including a few rudimentary ventral ones and several in process of 

 regeneration at other points, the number of branchia varies from 29 

 to 31. ^ Owing to excessive crowding some of them are forced inward, 

 producing an appearance of two series. The stems or radioles are re- 

 markably short, stout, rigid and brittle and, without considering the 

 rudimentary and regenerating ones, increase gradually in length from 

 ventral to dorsal, the latter being about i longer than fullv developed 

 ventral ones. Although the outer face is round, the basal J or so, dis- 

 tally to the position of the first eye, bears a pair of very low lateral 

 wmgs or margins which are united for a very short distance at the 

 base. Beyond this point the stems are laterally compressed. The 

 barbs are also thick and brittle, closely two-ranked, and all short, the 

 longest proximal ones not exceeding 3 times the diameter of the stem 

 and the distal ones being much shorter. A\rhen fully developed they 

 continue nearly to the end, leaving free a short thick tip only. Eyes 

 are exclusively in one series on the side of the stem nearest to the dorso- 

 median line. They are deep purplish-brown and very conspicuous, 

 and confined to a zone comprising the middle half of the branchiaj, but 

 most irregularly arranged on individual branchiie, on which they seldom 

 occupy the entire width of the zone, though they may be variously 

 scattered, or crowded into one or more groups. The usual number has 

 4 or 5, but varies from 2 to 9, and they may equal ^ the diameter of 

 the stem or be minute, scarcely visible specks, and all or any number 

 may be large or small. 



A high oral membrane with rumpled, sinuous margins begins ven- 

 trally at the sides of the mouth, is reflected on itself and passes around 

 the internal bases of the branchias to become continuous dorsally with 

 the large, much folded, foliaceous tentacles. 



The peristomial collar differs considerably from the structm-e typical 

 of the genus, as exemplified by P. reniformis and P. oculifera, and indi- 

 cates the method of transition between forms with the collar lobes 

 widely separated and those with them in contact dorsally. The dorsal 

 portion consists of a pair of very low folds reflected into the dorsal 

 fissure and there coming into contact. These are continuous with the 

 remainder of the coUar which rises abruptly into a pair of rounded lobes 

 just above the collar setae. From this point it is high and regular to 

 near the median ventral region, M^here a wide open notch on each side 

 partly separates the slender, pointed ventral lobes which are divided 

 from each other by the deep ventral fissure. 



