100 H. J. HANSEN. 
(The brood in the marsupium itself; no sexual difference in 
the mouth-parts.) 
It may be preferred first to deal with the genera of the two 
very small sub-families before proceeding to the rich sub- 
family, the Spheromine. 
Sub-family Limnoriine. 
Only one genus is known, the diagnosis of which may be as 
follows: Antennule and antenne very short, freely protrud- 
ing, their proximal joints not fitting in excavations on the 
head. Endp. of plp.! more than three times longer than 
broad ; exopods of all pleopods unjointed. Last abdominal 
segment with the posterior margin equally rounded, without 
terminal notch. Urp. with exp. much shorter than endp. 
Limnoria (Leach). 
Sub-family Plakarthriine. 
This sub-family is established on a single genus, the 
diagnosis of which is given here. ‘lwo proximal joints of 
each antennula, and third and fourth joints of the antenne 
exceedingly expanded in front, with their anterior margin cut 
off. All thoracic legs simple. Endp. of plp.! nearly four 
times longer than broad; exopods of all pleopods unjointed. 
Abdomen terminates in a nearly semicircular notch. Head 
and abdomen quite excluded from partaking in forming the 
outline of the animal; this outline is continuous, regularly 
oval, formed exclusively by the front margin of first and 
second joint of the antennule, third and fourth joints of the 
antenne, the outer margin of the thoracic epimera, and the 
distal margin of the uropods. Animals very depressed, the 
lower surface concave. 
Plakarthrium (Chilton) (Chelonidium (Pfeffer) ). 
Sub-family Spheromine. 
This rich sub-family is divided into three sharply defined 
groups. 
(A) Sph. hemibranchiate: Plp.* and plp.’ have the 
