ARTICULATA. 109 



American species. The name of the latter is changed from reticulata^ as 

 this has been ah-eady applied to a European species. 



Fam. 4. Aj^odida?. This family includes Latroilje's fifth order, PliylJo- 

 poda^ in which the body is either naked, inclosed in a bivalve shell, or with 

 the head and thorax covered with a carapace. The body is divided into a 

 great nui^bor of segments, most of which have foliaceous feet adapted for 

 breathing, the number of which varies from eleven to sixty pair. Antennas 

 two or four in number, and not adapted for swimming ; eyes two or 

 three. 



Ajms {pi. 78, fig. 25) has a large carapace covering nearly the entire 

 body ; one pair of short antennfe, and sixtj- pair of branchial feet. Schajffer 

 enumerated the number of pieces which enter into the composition of the 

 body, and found them to amount to 1,802.604. He found that each of the 

 caudal filaments in Apas cancrifor mis contains 480 articulations. It 

 inhabits fresh water ponds, and swims equally well with the back above or 

 below. It reappears in desiccated ponds in two days after a rain ; and it 

 has been found in ponds that have been without water for several years, 

 whence it may be inferred that the eggs retain their vitality for a long time. 

 They feed upon the microscopic Entumostraca, and are in turn devoured 

 by frogs. 



The metamorphosis of Ajyus is much like that of Cyclops, Leniica, etc. 

 When the young leave the q^^., the body is narrowed posteriorly, the tail is 

 wanting, the antennie are large, and the first and only pair of feet are 

 robust, and longer than the body, thus presenting opposite characteristics 

 from the adult. The length of the common European species, ^4. cancri- 

 fonnis., is two and a half, and the breadth one and a half inches. There 

 are but few species known. One has been described from the West Indies, 

 one from the eastern side of the Rocky Mountains, and another from the 

 Sandwich Islands. 



Brancldpus pisciformis {pi. 78,^^. 26) was described under this name, 

 according to W. Baird, by Sch^ffer, in 1752, and was subsequently named 

 Chirocephalus diaphanus.^ by Prevost. It has two j^edunculated eyes, four 

 antennoe, eleven pairs of branchial feet, and there is no shield. In the male, 

 the larger pair of antenme are prehensile, resembling mandibles, their base 

 is large and fleshy, and the outer joint curved and cylindrical. From the 

 base of these antennae arises a pair of large flexible proboscidiform organs 

 with their appendages, all of which are usually rolled u^) beneath the head. 

 In the female the large antennae have a singular structure, being short, 

 compressed, bent downwards, pointed at the end, and unprovided with 

 appendages. The species figured is more than an inch long, and is found in 

 pools swimming upon its back. As in nearly all the Entomostraca, the 

 branchial feet are kept moving continually. These animals swim with the 

 aid of the tail, darting through the water like small fishes. They feed upon 

 dead animal and vegetable matter. The female has an external branchial 

 sac, and the young undergo a metamorphosis. 



Limnadia is inclosed in a bivalve shell somewhat as in Cypris, but the 

 animal is larger, being nearly half an inch long. The American species, 



313 



