88 H. J. HANSEN. 
genera with the notch rather feebly or very teebly developed 
the mouth-parts are normal, in the genera with the notch 
rather deep or very deep and looking upwards the mouth- 
parts are metamorphosed, while in a few genera with the 
notch looking essentially backwards and at least of moderate 
depth the mouth-parts vary as to the feature in question. 
Considering the whole family, we arrive at the result that in 
all forms with the abdominal notch shallow or wanting in the 
females the mouth-parts are not metamorphosed; in the large 
majority of forms with the notch well developed, and in all 
forms having either a rather deep or very deep notch looking 
essentially upwards, or a notch divided by a mesia! process, 
the mouth-parts are metamorphosed; while only at most two 
genera with the notch well developed remain as being—at 
least for the present—apparent exceptions from the rule. 
Some remarks on the significance of the notch and on the 
remarkable connection between the shape of the end of the 
abdomen and the development of the mouth-parts in egg- 
bearing females are set forth in Chapter V. 
IV. Sexuat DirrerEnces. 
In most genera the adult males are larger, sometimes even 
much larger, than the females, in some nearly of the same 
size; in Cassidinidea ovalis (Say) I have found the ovi- 
gerous females larger thanan adult male. Of Plakarthrium 
typicum (Chilt.) I have seen several specimens of very 
different sizes from the same locality ; among the smaller 
specimens I found an adult male and a female with the marsu- 
pium complete, while a considerably larger specimen had 
rudimentary marsupial lamellee. 
~The adult males of all genera, Dynamene (Nesa) (Leach) 
and Ancinella (n. gen.) excepted, possess an oblong or 
very elongate, generally narrow, flat stylus, the ‘ appendix 
masculina,” proceeding from the inner margin—either near 
its base or sometimes at the end—of the endopod of plp.?;! 
1 On the following pages some abbreviations are generally used, viz. plp.’, 
plp.?, plp.®, for first to fifth pairs of pleopods, endp. for endopod, exp. for 
exopod, urp. for uropods. 
