investigation has brought several of them to life again, and 

 in this process the pleon, which at first glance would not 

 seem likely to offer differentiating characters of generic 

 value, has been latterly made to play an important part. 



Though the pleon throughout the family is dorsally very 

 compact, and in some species has all its segments coalesced, 

 there are many in which the segmentation is not entirely 

 neglected. The dividing line may either be dorsally complete 

 or limited to the sides, or dorsally expressed but laterally 

 incomplete. In Stoiosonia, Leach, and Erichsonia, Dana, 

 there are no such dividing lines. In Epelys^ Dana, and 

 Synidotea^ Harger, there are the lateral rudiments of one 

 line. A new genus, Paridofca, has one line and lateral 

 rudiments of two others. In Idotea, Fabricius, sensu 

 strictiore, there are two lines and one pair of lateral 

 rudiments. The same seems to be the case with CleaiitiSy 

 Dana, according to his account of the type species, but in the 

 figure three lines are shown in addition to the pair of 

 rudiments. In Edofia, Guerin-Meneville, there are three 

 lines. In Zeiiobiana^ Stebbing (n.n., 1895, for Zenobia, Risso, 

 1826, pre-occupied), there are three lines and one pair of 

 lateral rudiments. In CJiiridoten^ Harger, there are three 

 lines, with (or without) one or two dorsal rudiments. In 

 Glyptonotus, Eights, there are four lines. 



It is at once obvious that the character in question is not 

 sufiicient by itself for the delimitation of the genera, and it is 

 still uncertain whether it can conveniently be allowed any- 

 thing more than specific value, when all members of the 

 family are taken into consideration. In the genus CleantiSy 

 for example, its use will be completely nullified, if we accept 

 the extension given to that genus by Mr. E. J. Miers, who 

 includes in his generic definition a pleon " with all the 

 segments coalescent, or composed of two to five distinct 

 segments." But so wide or loose a characteristic seems more 

 proper to the definition of the family than of a single genus. 

 Suitably used, the segmentation of the pleon may prove a 

 very serviceable adjunct to other generic characters, among 

 which may be mentioned the extent and number of the side-- 

 plates in the peraeon, the one-jointed or many-jointed 

 flagellum of the second antennae, the number of distinct 

 joints in the maxillipeds, and the oresence or absence of the 

 second branch of the opercular uropods. 



Par IDOTEA, n.g. 



Side-plates of second and third peraeon segments not' 

 reaching to the end of the respective segments, Pleon with 

 one short basal segment and lateral divisions indicating 



