PACHYCEPHALA. 
295 
1. LtEMArgus muricatus. Tab. XXXIV, figs. 3, 4. 
Laimargus muricattjs, Kroyer, Tidsskrift, i, 487, t. 5, f. a, b, c, d. 
— M. Edwards, Hist. Nat. Crust., iii, 475, 
t. 89, f. 2. 
Description. — The female of this little animal is about 
ten lines, or nearly an inch in length, and of a light horny 
colour. The carapace or cephalo-thorax is considerably 
smaller than the rest of the body, and is studded all over 
with numerous small prickly tubercles. The elytraform 
plate and last thoracic segment are finely serrated round 
the lower margins, and are both deeply notched. The 
male is about half an inch in length. 
Hab. — On the Ortliagoriscus molce, or short sun-fish, 
W. Yarrell, Esq. 
Tribe 2—. PACHYCEPHALA* 
In the animals belonging to this tribe, the head is 
generally much smaller than in those of the preceding, 
and has not the broad, flat, shield-shaped form that these 
have, nor the lamellar plates on the front part, but is 
generally rather thick and obtuse. 
The antennae are much longer than those in the 
Peltocephala, and are composed of five and six, and even 
more, articulations. The thorax varies in the different 
genera, in form and in the number of articulations of 
which it is composed. The mouth-apparatus is generally 
less strongly developed in these genera than in the others, 
and the conformation of the foot-jaws is much less regular. 
The feet of the animals belonging to the Pachycephala 
differ also from those organs in the Peltocephala. They 
are not, as in these latter, attached to a basal joint, which 
extends across the under surface of the thorax in the 
shape of a broad plate, but have their basal joints detached 
from each other. They are all parasitic, and when young 
undergo a metamorphosis like the Cyclopidse. 
* VLaxvg, thick, and K£0a\>/, head. 
