430 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxm. 



setsB are longer; this causes these young females to look much like 

 males, and it deceived even so good an observer as Kroyer. But a 

 careful examination of the genital segment reveals the presence of 

 cement glands and sperm receptacles, and thus precludes any idea 

 that these are males. 



This species is found upon the gill arches of the common sand 

 shark, Carchanas littoralis, rarely upon the floor or roof of the mouth. 

 In nearly every instance it is solitary, a single female being fastened 

 to either the fifth or the fourth arch on the posterior side, so that all 

 one can see of it on looking down the shark's throat is the white or 

 brownish egg-strings. 



They are fastened rather more securely than Pandarus, by means of 

 their second maxillipeds, and it requires considerable effort to dislodge 

 them. On being removed to an aquarium it is found that the females 

 can not swim, but are fully as helpless as the other genera in this sub- 

 family, lying upon their backs and keeping their swimming legs in 

 constant motion. They can be kept alive for a longer period than 

 Pandarus, however, and seem much more hardy. The anterior por- 

 tion of the body, including the carapace and free thorax segments, is 

 very transparent and colorless. Hence it would be diflicult to (Hstin- 

 guish the animal against the white background of the shark's throat 

 were it not for the fact that the digestive tube is dark colored, the 

 coiled oviduct in the genital segment is brown, and the egg-tubes are also 

 brown. The latter arc long and slender and appear fragile, looking as 

 if they would pull apart on slight provocation; but the very reverse 

 is ft)un(l to be true. Indeed they are so tough that the body of the 

 female will pull apart at the fourth segment before the egg-strings will 

 break. 



In the living copepod these egg-strings are always encased in a 

 heavy layer of mucus obtained from the shark's gills, and they often 

 have in addition a growth of algse or other foreign matter mixed with 

 the mucus. When these substances extend up onto the genital seg- 

 ment of course they help to hold the egg-strings in place. But it not 

 unfrequently happens that they fail to reach the genital segment, and 

 in that case the egg-strings have to hold the entire mass in place. As 

 the copepod is almost always found on the insitle of the gill arches, 

 or at least with the posterior part of the body and egg-strings on the 

 inside, it must be subjected to more or less friction from the convul- 

 sive movements of the living fish upon which the shark feeds. 



The utility, therefore, both of the heavy coating of mucus over the 

 egg-strings, and of their secure attachment to the genital segment, 

 becomes very apparent. The males are good swimmers and very 

 active, like other Nogaus species, and in the aquarium they move 

 about restlessly. 



