THE OSTRACODA 



793 



The first pair of maxillae (Fig. 1245 c) is formed of a thick, mus- 

 cular, basal part, from the extremities of which four digitiform 

 processes originate. The larger of these prominences (Fig. 1245 ^0 

 is jointed and movable and must evidently be regarded as a palp, 

 whereas the three remaining form the immediate continuation of 

 the basal part and are the true masticatory lobes. The first one of 

 these is usually armed with two strong spines (Fig. 1245 c^ and Fig. 

 1270 e) which may or may not be toothed, and are regarded as of 

 specific importance. To the outer side of the basal part a large 



Fig. ia4S. (o) Lower lip or labium; (6) Mandible with palp; (c) First maxilla with branchial plate; 

 (d) ^cond maxilla of female with palp {Cypris incongruens). 



semilunar lamella (Fig. 1245 c^) is attached, which is generally called 

 the branchial plate. This plate may be seen to move rhythmically 

 in the living animal, and is for the purpose of renewing the supply 

 of fresh oxygen-laden water within the shell cavity. It is directed 

 obliquely upwards and exhibits along the posterior edge a series of 

 dense and regular finely plumose setae, from x6 to 20 in number. 



The second pair of maxillae (Fig. 1 245 d) consists of the same 

 principal parts as the first, though different in appearance. The 

 basal part (Fig. 1245 d^) is much smaller, not divided at the end, and 

 terminating in a single masticatory lobe. The branchial lamella 

 (Fig. 1245 d^) are usually semicircular and provided with a few plu- 

 mose setae, while the palps (Fig. 1245 d^ and Fig. 1299 d-e) are of 



