PACKAED.] PHYLLOPODS OF NORTH AMERICA. 297 



his order Phyllopoda iuto two suborders, Cladocera and Brancliiopoda. 

 Gerstaecker in Bronn's Classen und Orduungen Arthropoden, 186(3-'79, 

 adopts the order BrancMo])oda, and divides it into three suborders, Os- 

 tracodeaj Brancliiopoda genuina^ comprising the Cladocera^ Phyllopoda 

 of other authors, and the Brancliiura (Arguhis, &c.). 



In 1879 the writer, in his " Zoology for Colleges," adopted the order 

 Branehiopoda, with three suborders, viz, Ostracoda, Cladocera, and Phyl- 

 lopoda. 



Suborder PHYLLOPODA. 



In this group the body is usually (the Branchipodidce excepted) in 

 part covered by a large carapace (the mandibular segment greatly de- 

 veloped tergally), which is in the lower forms (Limnadiacea) bent down, 

 forming two valves, connected by a true hinge, and opening and shutting 

 by an adductor muscle, so that the shell resembles that of a bivalve 

 mollusc, such as the fresh-water Cyclas and Pisidium. They have two 

 pairs of antennse, a pair of mandibles, and two pairs of maxillre, and 

 in Apodidce a pair of maxillipedes. The name of the group, Phyllopoda^ 

 is applied to them on account of the feet, which are broad and leatlike, 

 with a series of six primary inner lobes or endites and two exites, the latter 

 forming a gill and accessory gill or fiabellum. The abdomen is not clearly 

 differentiated from the thorax, and the abdominal feet are not different 

 in shape from the thoracic appendages. The number of body-segments 

 varies more than in anj' other group of genuine Crustacea, there being 

 seventeen in Limnetis and sixty-nine in Apus, or over three times as 

 many as in the lobster or Decapods in general; the segments are thus 

 often irrelatively repeated, a sign of inferiority. The eyes are either 

 sessile and united into a single mass, or, in the highest family {Branchi- 

 podidw), they become stalked, thus anticipating the stalked eyes of the 

 Decapoda. The telson is usually large and spiny, bearing in all the 

 genera a pair of caudal appendages probably homologous with the limbs. 



All the members of the ^iborder hatch from the egg in the Nauplius 

 form, like that of the Copepod Crustacea, with some differences, all 

 having three pairs of appendages corresponding to the two pairs of 

 antennse and mandibles of the adult. 



The species for the most part live in pools of fresh water liable to 

 dry up in summer; those of Artemia live in brine pools and lakes. The 

 eggs, after being fertilized and borne about for a time under the shell 

 or in egg-sacs, are finally suffered to drop to the bottom of the pond; 

 here they lie after the water of the pond has eva^^orated, the eggs re- 

 maining in t'de dry mud until, the ponds having been refilled by the 

 autumn rains, the young hatch out and the cycle of life begins anew. 



Family L LIMNADIADJE Baird. 



LimnadiadoB Baird, Proc. Zool. Soc. London, XVII, 86, 1849; Ann. & Mag. Nat. Hist. 



2d Ser. XIV, 229, 1854. 

 Estheriadcv Packard, Hayden's U. S. Geol. Surv. Ter., for 1873, 618. 1874. 



Body inclosed in a bivalved shell ; head usually with a large ros- 

 trum; eyes compressed, small, sessile, closely contiguous or united. 1st 

 antennoe minute, Sjointed or multiarticulate, the segments not being 

 well marked; 2d antennse large, with two flagella, each consisting of 

 from 9 to 20 joints. A pair of mandibles; one or two pairs of maxillse ; 

 10 to 27 pairs of swimming phyllopod feet, each with six lobular endites, 

 and a gill and fiabellum divided into two divisions, the upper in the fe- 



