4 PEOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



study, and comparisons of a number of specimens of each species; and 

 the specilic characters here presented and figured were found to be con- 

 stant, and apply to all sizes. 



The family characteristics are as follows : 



Head broad and rounded above, tapering below to the oral appara- 

 tus. Eyes on the dorsal and lateral surlaces of the head. Both pairs 

 of autenuaj present in the male, and long; in the female the inferior 

 pair obsolete, and the superior pair short. Thorax broad anteriorly, and 

 tapering posteriorly. The first and second pairs of thoracic feet short; 

 the extremity of the fourth joint being more or less produced, and the 

 fifth joint with a pair of wing-like appendages on either side of its 

 apex. The fifth pair of thoracic feet developed into a stout, prehensile 

 organ. The remaining pairs of feet simple. Abdomen narrow. The 

 caudal appendages slender, cylindrical, and two-branched. 



There is a very marked resemblance among the Phrommidce. The 

 family characters are many; the generic and specific characters are 

 few, but constant. 



The eggs of the female are carried in an incubatory pouch between 

 the posterior thoracic feet. Females with the young in every stage of 

 development within the eggs may be found swimming free; yet when 

 the young leave the eggs, they are always found, I believe, inside the 

 body of a Fyrosoma, a Beroe, or a Medusa, which the female am])hipod 

 appropriates as a home for her immature species. The parent and young 

 are usually found inclosed in the same case. The former by this action 

 manifests, apparently, a maternal solicitude for the welfare of her off- 

 spring. This is interesting as appearing in animals so low in the scale 

 of being as the am])liipods. 



There was observed a great disparity between the number of males 

 and females collected in any locality. In the preparation of this article 

 there were examined forty-five specimens belonging to the different ge- 

 nera of the family, and the proportion of males to females was found to 

 be as 1 to 8. Until quite recently the male form — being so different — was 

 not recognized as belonging to the same species. The discovery Avas 



made by Clans. 



Phronima, Latreille. 



Head, thorax, and abdomen as described under Phronimidcv. The 

 first and second pairs of thoracic feet short and slender, with the fourth, 

 or carpal joint hroadhj liroduccd; the third and fourth pairs long, sim- 

 j^le, and subequal. The fifth pair stoutly developed, and provided with 

 a strong ineliensile organ, resemhling the claw of some of the Cancridw. 

 The last two pairs of legs shorter than the preceding, and subequal. 

 The three pairs of caudal appendages long and slender, each furnished 

 with two lanceolate branches. Telson short. 



Sexual differences. — Males smaller than the females. In the female 

 the inferior antennre are absent. In the position of these organs — be- 

 neath the lateral eye — is a broad, rounded prominence, slightly pro- 

 jecting beyond the anterior margin of the head. The apex of this 



