MARINE ISOPODA OF NEW ENGLAND, ETC. 391 



find of moderate size, not being greatly enlarged. The pleopods arc 

 destitute of cilia in tlie ndults. 



Tliis family is evidently closely related to the preceding and may yet 

 have to be united with it, or even be extended so as to include also the 

 Cirolanidcc. Our representatives of the three families are so few that 

 I have had little opportunity to study the genera, and as before stated, 

 I have separated the Cirolanidce priucii^ally in deference to the opinions 

 of Schiodte. Alitropus Edwards, Syscenus Harger, and ^(jathoa Dana 

 may be mentioned as genera pointing toward a transition between the 

 ^gidcc and Cymothoidcc, and it is evident that the latter family is made 

 up of forms degraded by parasitism. They have thus exchanged the 

 ambulatory legs of the ^gidcc for strictly ancora.1 legs, for the most part 

 in seven pams, and have lost the natatory cilia of the pleopods. Their 

 antennary organs are also much less iierfect than in that family. All 

 these modifications are in the line of the sedentary life of a iiarasite. 



The interesting observations of Mr. J. F. Bullar have shown that in 

 certain genera of the Cymothoidce {Cymothoa, Xerocila, AnUocra) a peculiar 

 form of hermaphroditism occurs, the young at a certain stage of devel- 

 opment being males with well developed testes and external organs, 

 but possessing at the same time ovaries with the oviduct ending blindly. 

 As development proceeds the male organs are lost by molting, the ovi- 

 duct obtains an external opening, the incubatory pouch is developed, 

 and the animal becomes a fem?Je. Mr. BuUar's statements provoked 

 considerable discussion, but they have recently beeu verified by Mayer, 

 who has, however, shown that self-fertilization does not occur. 



Three genera of Cymothoidw are represented within our limits by as 

 many species, and a fourth species, Cymothoa irrmgufitator Say* (La- 

 trobe) may yet be found, being not a rare parasite in the mouth of the 

 menhaden [Brevoortia menhaden Gill) in southern waters. The projec- 

 tion of the front of the head over the bases of the antennary organs, 

 and the strongly hooked or ancoral legs are characteristic of the family, 

 and the genera may be distinguished by means of the following table : 



c ciliated, eyes large conspicuous, JEgathoa, p. 393 



Uropod8< Tj. 1 . -1 -1 < symmetrical; posterior epimera elongated, Ncrocila,-^. 2Q\ 



\ ' i unsymmetrical; ejiimera short, Xu'OHCcrt, p. 394 



Nerocila Leach. 

 NerocUa Leach, Diet. Sci. nat., tom. xii, p. 351, 1618. 



Body oval; head small; eyes of moderate size; posterior thoracic seg- 

 ments and epimera angulated or spiniform, giving a sharply serrated 

 or dentated outline to the thorax; first two "abdominal epimera" also 

 spiniform; pleon of six distinct segments. 



Our species of Nerocila has the characters of the genus much less pro- 

 nounced than some foreign ones, as the posterior epimera are nearly 



*Jour, Acad. Nat. Sci. Phila., vol. i, p. 395, 1818. 



