FAMILY SPHMROMIDA. 75 
one, viz., Cassidinini. Their number is always three 
pairs; they belong to the second, third, and fourth 
pairs of legs. Inthree genera—Hxospheroma (Stebb.), 
Tsocladus (Miers), and Zuzara (Leach)—all belonging to the 
hemibranchiate Spheromine, they are so small that they are 
far from reaching each other from the two opposite sides ; in 
all other genera they overlap each other at least somewhat, 
and generally considerably, or sometimes very much along 
the mesialline. Inthe forms with brood of the section Cassi- 
dinini seen by me the marsupial lamelle are wanting; 
this curious feature is discussed in the sequel. 
Of the sub-family Limnoriine Limnoria lignorum 
(Rathke) has been examined. ‘lhe number of eggs is rather 
moderate (twenty-nine were found in one specimen); the 
eggs are enclosed in the marsupium itself. The volume of 
each full-grown young one is very considerably larger than 
that of an egg; the marsupium containing such larve is 
accordingly exceedingly distended, more than twice as deep 
as in a female with eggs recently laid. The marsupial lamellee 
are exceedingly large; the marsupium covers the whole lower 
surface of thorax. 
Of the sub-family Plakarthriine, a single small female of 
Plakarthrium typicum (Chilt.) has been examined. The 
marsupium reaches nearly to the base of abdomen, but its 
lamellze overlap each other only very moderately. It con- 
tains in my specimen five very large eggs still nearly circular; 
there is plenty of room for their development in the flat mar- 
supium. Judging from the shape and the biology of the 
animal, this shape of the marsupium is scarcely much altered 
during the development of the brood. The third sub-family, 
the Sphzromine, present various modes of development of 
the brood. 
Of the hemibranchiate Spheromine I have seen adult 
females of eight genera; of two genera, Hemisphewroma 
(n. gen.) and Cassidinella (Whitel.), they are unknown, but 
the former genus is closely allied to Spheroma (Bosc); 
Cassidinella seems to be only a sub-genus of Cymodoce 
