1889.] ON SOME JfBESH WATER OSTEACODA AND COPEPODA. 13 



and reaching to the lower edges of the valves. It is about half 

 as long as the corpus and composed of 4 joints, the two first 

 of which, however, are less distinctly defined. Of the joints the 

 basal one is much the largest and bears on the outer side 

 a narrow plate, the so-called branchial appendage, pointing 

 obliquely upwards and provided at the tip with about 5 very 

 strong and densely plumous setae; along the posterior edge this 

 joint has 3 thick setae provided with unusually long cilia at 

 the edges. The 2nd joint is quite short and bears at either 

 edge a bunch of long slender bristles, 3 anteriorly and 4 poste- 

 riorly. The 3rd joint is almost twice as long, but considerably 

 narrower and somewhat tapering to the extremity ; it is likewise 

 provided at the end on either side with a fascicle of setae, but 

 rather smaller than those on the preceding joint. The last joint, 

 finally, is very small and terminates with several, partly ungui- 

 form bristles. 



The 1st pair of maxillae (PI. Ill, fig. 6, PI. 4 ; fig. 1) exhibit 

 a thick muscular basal part, from the extremity of which 4 

 digitiform processes are seen to originate, pointing obliquely 

 forwards to the oral orifice. The foremost of these processes is 

 movably articulated to the basal part and consists of two well 

 defined articulations, the first narrow cylindrical and at the end 

 anteriorly provided with about 4 curved bristles, the last rather 

 small, almost quadrangular and terminating with several strong 

 curved bristles, shorter than those on the preceding joint. This 

 process must evidently be regarded as a palp, whereas the 3 

 posterior processes, forming the immediate continuation of the 

 basal part, are the true masticatory lobes. The latter are much 

 shorter than the palp and successively diminish in size posteri- 

 orly ; they are at the tip provided with a dense bunch of strong, 

 partly spiniform bristles, and the foremost lobe has besides a 

 few ciliated setae affixed to the anterior edge. To the outer 

 side of the basal part a large, semilunar lamella is attached, 

 generally termed the branchial plate. This plate, which in the 

 living animal is seen moving in a rhythmical manner in order 

 to renew the water within the shell-cavity for the purpose of 



