94, H. J. HANSEN. 
posterior part of abdomen consists of only one segment, the 
sixth; the anterior part must consequently correspond with 
the five anterior segments in Limnoria. In Spheroma, 
Cassidinopsis, and numerous other genera, this anterior 
part has on the upper surface three sutures as rudiments of 
division into seements; the anterior of these sutures is entire, 
the two other completely vanished at the middle. Four seg- 
ments are thus traceable, but as the part corresponds with 
five segments we must conclude that one segment, perhaps 
the first, has completely disappeared. In Vireia burgunda 
(Dollf.) (but notin V. berica (Fabiani) ) and in Coecosphe- 
roma Virei (Dollf.) the two parts of abdomen are immovably 
fused with each other. 
The pleopods are mentioned by various authors in the 
descriptions of some genera or species ; it has been observed 
that the five pairs of an animal are not similar and that, for 
instance, fourth and fifth pairs are not uniformly built in all 
forms. But no author has undertaken a real comparative 
study of these appendages, which in reality afford characters, 
not only for genera, but for groups of genera; the omission 
of this study is a principal reason, not only for the complete 
want of grouping of the numerous genera, but for a good 
deal of the confusion as to the reference of species to genera. 
In the following I use the most important differences in the 
pleopods as characters in the diagnoses of the sub-families, and 
especially as the base for dividing the Sphzrominz into 
ercups of genera; other differences are used in establishing 
sections of genera or in the analytical keys, sometimes even 
in the diagnoses of genera. In this paper I omit here a 
more detailed account of these appendages, thinking that a 
perusal of the diagnoses in the next chapter may convey 
sufficient knowledge of their structure and the numerous 
differences observed. It may, however, be added that, for 
instance, the thickened areas or real protuberances—clothed 
with spines—on the exp. of plp.* in almost all Sphero- 
mine afford more characters than those mentioned in the 
following treatment; further elucidation of this and other 
topics must be postponed to the illustrated paper. 
