746 CRUSTACEA. 



formes. Appendices caudales margini abdominis laterali per ramum 

 internum conjunctas. Antennae ad frontis marginem capitis affixae, 

 apertae. Abdomen 1-2-articulatum. Pedes non ancorales [raro 4 

 antici ancorales]. Branchiae ciliatae. Epimerae non distinguendae. 



The Cymothoidae, in their non-ciliate branchiae and simply oper- 

 culiform maxillipeds, appear to rank first in this subtribe. The high 

 value of this non-ciliate character of the branchiae in fixing the rank 

 of the species, is apparent from the fact, that they are in this parti- 

 cular farthest removed from the Amphipods. In the passage to the 

 Amphipod form, the first step is a ciliation of the margin, the next, 

 an elongation of form, and finally appears the oblong natatory shape. 

 The Cymothoidae pass into the iEgidae through certain species of the 

 former group (iEgathoinae), in which the caudal pair of abdominal 

 appendages is ciliated, as in the iEgidae, though not the branchial 

 pairs. 



The iEgidae, hitherto ranked in the same family with the Cymo- 

 thoidae, have, in fact, an intermediate character between them and the 

 Spheromidae. Like the former, it is true, they have the caudal stylets 

 free, and not attached by one of the plates to the abdomen ; besides, 

 the joints of the abdomen are free, and there are distinct thoracic 

 epimerals : but in other important characteristics they are Sphero- 

 moid. For example, the antennae are attached to the front margin of 

 the head, and not to its under surface; the branchial leaflets are 

 ciliated ; the maxillipeds have usually the full number of joints, 

 although unlike those of the Spheromidae in being broad and short ; 

 the feet are not all ancoral, only the six anterior pair at the most 

 having this character. The Spheromidae are peculiar in their one or 

 two-jointed abdomen, the more elongated palpiform maxillipeds, the 

 absence of distinct epimerals, and in having the caudal stylets fixed 

 by the inner plate to the side of the abdomen. 



The following are the subfamilies and genera of these groups : — 



Fam. I. CYMOTHOID^]. 



Subfam. 1. CYMOTHOINiE. — Lamellae caudales nudae. Abdomen 

 multiarticulatum, segmentis liberis. 

 G. 1. Cymothoa, Fabr. — Femora lata, posteriora latissima. Segmenta thoracis 



