26 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 121 



taxonomy of the genus in confusion. Of all of the species, P. instructa 

 Wilson is by far the most easily recognized, and the characteristic 

 ramshorn-shaped attachment structiu-es show little variation in the 

 specimens present in the U.S. National Museum. Yamaguti's iden- 

 tification of Japanese pennellids from Xiphias gladius as P. instructa 

 (1939b) may warrant some question although there is more evidence 

 for his identification, from his figure (pi. 33, fig. 193) and from the 

 host, than there is for the inclusion of other material in the species. 



The original description of P. histiophori Thomson, 1889, indicates 

 some differences between the type material and that here described. 

 P. histiophori is figured as having a larger rounded protuberance on 

 the ventral surface, between the bases of the attachment structures, 

 the 4 pairs of thoracic legs appear to be more closely grouped, and the 

 pedigerous area of the neck appears more swollen and distinct from 

 the rest of the neck. The size of the minute ventral protuberance 

 between the bases of the attachment structures is variable in the 

 3 specimens examined for this description, and there is variation in 

 the size, shape, and position of numerous small irregularities on the 

 cephalothorax. The grouping of the thoracic legs may be distinctive 

 although Thomson's original figure is not clear enough to offer 

 grounds for separation. The difference in the size of the pedigerous 

 region of the neck and the distinction of this region from the rest of 

 the neck may, based on an examination of the variation in some of 

 the other members of the genus, be due to intraspecific variation. 



Pennella species 



Material. — One complete and 1 incomplete (abdomen missing) non- 

 ovigerous female (USNM 112872) from the external surface of Remo- 

 ropsis brachypterus (Solander) collected by the USFWS from the 

 stomach of a yellow-fin tuna, Neothunnus macropterus (Schlegel), cap- 

 tured off Hawaii. 



Measurements. — (In mm) females: 



Greatest length of body (N=l) 35.85 



Length of cephalothorax (N=2) 4.00, 3.75 



Width of cephalothorax (N=2) 2.85, 3.00 



Length of neck (N=2) 10.88, 12.75 



Width of neck (N=2) 1.65, 1.35 



Length of trunk (N=l) 21.00 



Width of trunk (N=l) 1.50 



Approximate length of abdominal pluinosities (N=l) 7.13 



Length of attachment structures (N=2) (2.25, 2.25), (3.15, 4.05) 



Description. — Cephalothorax (figs. 10a, b) presumably consisting 

 of cephalon and first thoracic segment although maxOlipeds not dis- 

 cernible. Pair of long, dactyliform attachment processes present 

 immediately posterior to cephalothorax. Cephalothorax with 2 types 



