MAEINE ISOPODA OF NEW ENGLAND, ETC. 377 



* 



dactyli found in the JEgidcc, and still better developed in the Cymothoidce. 

 In the Cirolanidw the propodus, in the first three pairs of legs, is some- 

 what curved and the dactyli are nearly straight, so that while the first 

 three pairs of legs are powerful organs of prehension, they are also 

 capable of letting go preparatory to the seizure of another victim. The 

 posterior pairs of legs are ambulatory or fitted for swimming by their 

 form and armature of bristly hairs. The ciliated pleopods are also 

 powerful swimming organs, so that these animals are well fitted for the 

 predatory life they lead. The epimera are well separated by sutures 

 in all the thoracic segments behind the first. The pleon is scarcely nar- 

 rower at base than the last thoracic segment, and is composed of six 

 distinct segments, of which the last is much the longest, but not broader 

 than the preceding segments, and tapers posteriorly. The uropods arc 

 lateral, articulated near the base of the last segment and distinctly 

 biramous. 



The mouth-organs of this and the two following families have been 

 the object of special research by J. C. Schiodte, whose papers in the Natur- 

 historisk Tidsskrift have been in part translated in the Annals and 

 Magazine of Natural History. He regards Girolana as representing " the 

 highest development of the crustacean type among the Isopoda," and 

 even hints that Cirolana and JEga should be removed to opposite ends of 

 the series of Isopoda. The same author would closely unite the Bopy- 

 ridcc, JEya, and the Cymothoidce into a single group, the Cymothoce, 

 while acknowledging that the young of Cymotlioa oestrum, " according 

 to the classification hitherto current, * * * would rather be allied 

 to Cirolana than to Cymothoa." His classification, however, appears to 

 be based almost entirely upon the structure of the mouth, disregard- 

 ing the totality of structure upon which alone morphological classi- 

 fication can securely rest. In deference, however, to his views I have 

 here regarded Cirolana as the type of a distinct family, which must still 

 be considered as closely related with the two following families, on the 

 principle that it is " more important that similarities should not be neg- 

 lected than that differences should be overlooked." 



Among the more important of the similarities by which these fami- 

 lies seem to be united may be mentioned the following, as exemplified 

 by our species. The segments of the thorax and pleon are all distinct 

 from each other, so that the body, in the adults, appears to consist of 

 thirteen segments behind the head, although in the genus OurozeuTctes 

 Edwards* the segments of the pleon are consolidated. The epimera 

 are distinct in all the segments behind the first thoracic. The pleon 

 may or may not taper from the base, but it is terminated by a large 

 scutiform segment, sometimes more or less sculptured, and bearing at 

 the sides, near the base, a pair of uropods, in which the basal segment 

 is more or less oblique distally and the rami lainelliforrn, though one of 

 them may be narrowly so. The pleopods are unprotected by any form 



* Hist. nat. des Crust., tome iii, p. 275, 1840. 



