THE OSTRACODA 805 



finest needle is scarcely efficient as a dissecting instrument. Either 

 of the above two mounting media bring out to view even the finest 

 hairs or ciliated structures. Alcohol or water are not advisable as 

 dissecting media and should be risked with few specimens. Fur- 

 thermore, Farrant's medium makes a very good permanent mount, 

 providing there is not too much on the slide. Either medium 

 should be added to the slide in small drops, then spread out in a 

 thin layer before attempting to dissect therein. It is commonly 

 best to make a preliminary examination of the dissection with a 

 f-inch objective, to see that the mount has been well prepared 

 and arranged. If so, add a small additional amount of the me- 

 dium, cover with cover glass, and the mount is permanent, pro- 

 vided the work is neatly done, too much medium is not added, and 

 the mounts are kept stored in a horizontal position when not in use. 



The valves should be preserved entire, if possible, and removed 

 to one side of the slide for further study. It is often desirable that 

 they be removed to a separate slide and mounted in balsam; es- 

 pecially if the slides are to be permanent and subject to much 

 handling. 



Drawings as well as study of a side view should always be made 

 from one of the valves, rather than from the entire specimen, as 

 otherwise a distorted view is likely to result. 



The dorsal view is more difficult to get indeed, it is often 

 advisable not to attempt it. Unless this view is obtained directly 

 above the specimen, it is worthless. Sometimes one valve alone 

 may be used by fastening it to a needle or similar object, and 

 then studying while covered with glycerin, or, if the valves are 

 dissimilar the entire animal may thus be mounted so that an 

 exact profile may possibly be obtained. It is indeed often pos- 

 sible to get very good dorsal profiles from many specimens while 

 they are in alcohol and glycerin in a Syracuse watch glass. 



The following characters have been retained as of most value 

 in the following key: presence and length of natatory setae of 

 the second antennae, segmentation of the second antennae, form 

 and number of spines of the first maxillary process, armature of 

 the second leg, arrangement of the spermatic glands, and armature 

 and shape of the furca. 



