IMMATURE SPECIMENS OF PENELLA FILOSA. 2Q/ 



are tuberculated. Behind the " head " the praethorax bears four 

 pairs of minute limbs and forward from the anterior pair of these 

 a stout, blunt "horn" projects on either side. This arrange- 

 ment of horns, however, is not invariable and out of thirty speci- 

 mens at my disposal from Ortkagoriscus niola I found nine with 

 an additional dorsal horn. A similar variation in the number 

 of the horns was noted in Patella varians by its describers 

 (Steenstrup & Liitken, '61) and parallel conditions are frequently 

 met among parasitic Copepoda which attach to their hosts by 

 analogous structures. A typical specimen of the Lernaeenicus 

 of the Menhaden for example --L. radiants- -has five simple 

 horns ; but specimens are commonly taken which possess a 

 greater or lesser number of these Jiaftorgane and not infre- 

 quently they are forked or are rough with small branches. 



The immature Pcnclla in the collection loaned me were five in 

 number. To these a young Pcnclla filosa taken from a sword- 

 fish brought into Woods Hole has been added, so that my series 

 included six specimens. The youngest individual (/4) (Fig. i), 

 had a distinct cylindrical cephalothorax, highly convex, with a 

 double-lensed median eye near the anterior end. Beyond the 

 border of the cephalothorax the three-jointed (?), hamate second 

 antennae projected. This cephalothorax was flecked with consid- 

 erable black pigment. The filiform thorax extended to a length 

 thirty-two times that of the cephalothorax. It was not seg- 

 mented but ringed as in the adult with indistinct circular constric- 

 tions near the hinder end. The abdomen was filiform, bore 

 along its sides twenty-two pairs of short unbranched lateral 

 appendages and terminated with a deep notch. On either side 

 of this was a small bisetose appendage. The first pair of 

 antennas were delicate, two-jointed, and setose. A prominent, 

 urn-shaped rostrum with a reflected, finely serrate border pro- 

 jected from the venter of the cephalothorax and was flanked 

 by reduced maxillae in the form of minute palps each tipped 

 with two delicate bristles. No traces of mandibles were found. 

 Just behind the rostrum in the mid-line there was a prominent 

 rounded tubercule and on either side of this the two-jointed 

 maxillipeds were situated. Further back, two shallow depres- 

 sions and back of these two larger shallow pits were visible. 



