640 CLASS X. 
Thoracica three families are included—the Balanide or sessile Cirri- 
peds, the Verrucide, (the genus Clysia Lracn, Creusia Lam., Ver- 
ruca SCHUMACHER, Scuum. Hssai d’un nouveau Systeme des Habita- 
tions des Vers testaces, 1817. Copenhav.), remarkable for their 
quite asymmetrical shell, and the Lepadide or pedunculated Cir- 
ripeds. In the second order of Abdominalia the seventh or last 
cephalic segment is quite distinct, and bears rudimentary organs 
answering to the first pair of foot-jaws in ordinary crustaceans, 
of which organs, and of the segments supporting them, there is 
no trace in the Thoracica; the seven succeeding thoracic seg- 
ments are destitute of any appendages; but the three segments 
of the abdomen bear three pairs of cirri. In the metamorphosis 
all the first changes are merely indicated by changes of form 
in the egg-like larva, without the development of distinct organs, 
and the last or pupal condition, which is attained within the sac of 
the parent, is very peculiar from the entire absence of rotatory 
limbs. There is only one genus Cryptophialus Darwin, and one 
known species Cryp. minutus Darw., Balanide, p. 566, Tab. 23, 
24. The third order Apoda is the most peculiar of all, it resembles 
the larva or maggot of a fly, the carapace is reduced to two separate 
threads for attachment. The last cephalic, the seven thoracic, and 
the three abdominal segments are all destitute of appendages. The 
single known species, Proteolepas bivincta, is parasitic within the sac 
of Alepas cornuta, Darwin Lepadide, p. 165, Tab. 3, fig. 6. See 
Darwin Balanide, pp. 20—22.] 
OrpeR V. Cladocera Latr. 
Body compressed, included in a horny shell, divided into two 
parts by a dorsal fold, without hinge. Head free, produced below, 
terminating in a species of rostrum. ‘T'wo small antenne at the 
apex and two larger at the base of head, split into two or three 
branches. Feet foliaceous, with four or five pairs. Abdomen ter- 
minated posteriorly by two setaceous appendages. 
Family XI. Daphnidea Straus. The characters of the order 
are those of the single family. Single compound eye. Larger 
antenne ramose, serving like oars for swimming. Ova in females 
situated on the back in a space between the shell and the segments 
of the thorax. 
Polyphemus Munu., Cephaloculus Lam. Eye single, large, 
occupying almost the whole head. Larger antenne bifid. Feet 
eight, exsert from shell. Tail reflected, bisetose at the apex. 
