

PHYLLOPODA. 



1307 



This is a peculiarity found in no other Entomostraca. It appears, 

 therefore, that Nebalia is properly associated with Chirocephalus in a 

 common tribe, and the two represent separate families in that tribe. 

 Of the other Phyllopods, Limnadia is built on the Cypris type in its 

 abdomen and other parts, and is far remote from Nebalia; and Apus 

 on the Limulus type in many points of its structure, although diffe- 

 rent in its mouth. These, therefore, cannot with propriety be asso- 

 ciated with Nebalia in a common group. 



Dr. Baird, in his British Entomostraca, makes the higher subdi- 

 visions of the Phyllopoda, family divisions. The distinctions among 

 them, as we have shown, are as great, at least, as those of the Cypris, 

 Daphnia, and Cyclops groups in the Lophyropoda. 



The homologies of the Limnadiae may be elucidated by a com- 

 parison of the structure with that of Cypris. In Limnadia, and also 

 Limnetis, an allied genus, the eighth and ninth pairs of legs have 

 a slender appendage, which extends upward into the ovarian cavity 

 over the back of the animal beneath the shell. In Cypris and Cypri- 

 dina, the posterior pair of legs is adapted to the same function, and in 

 the latter genus the organ is flexible, as in Limnadia. 



Now, in both Cypris and Limnadia, there are a pair of mandibles 

 and one of maxillae, which of course correspond in the two genera. 

 In Cypris, there are then three pairs of organs following, the last of 

 which has the ovarian use alluded to. In Limnadia, pairs of folia- 

 ceous legs follow the maxillae, the eighth and ninth of which have the 

 ovarian appendage. If now each pair of legs in Cypris corresponds to 

 three pairs in Limnadia, as suggested on page 41, the ovarian legs 

 will have normally the same relation in both. The corresponding 

 parts will be as follows : — 



Cypris, 

 Limnadia, 



i. 

 mand. 

 mand. 



II. 



max. 

 max. 



in. 

 max. 



IV. 

 1 pair feet. 



V. 



ovarian feet. 



pairs feet. 3 pairs feet. 3 pairs (2 ovarian). 



It is altogether probable that this is the true relation of the parts. 

 In this case, in Limnadiae having eighteen or twenty-one pairs of feet, 

 there will be three or four additional normal pairs of feet represented, 

 beyond the Cypris number of appendages, making the number found 

 in the Cyclopidae; and when, as in Limnetis, there are but twelve 

 pairs, three of which are posterior to the ovarian pairs, there is but 

 a single pair represented additional to the Cypris number. 



