118 CRUSTACEA——PERACARIDA CHAP. 
miles to the west of Melbourne. Although plainly belonging to 
the Anaspidacea, this interesting little animal, which only 
measures a few millimetres in length, and follows a similar habit 
to Anaspides, running about with its body unflexed, differs from 
all the other members of the Division in possessing sessile 
instead of stalked eyes, in the first thoracic segment being fixed 
to the head, and in a number of minor anatomical points. 
It is impossible at present to assign the Carboniferous forms 
(Gampsonyx, Palaeocaris, etc.) to their exact position in the 
Division, but it seems that they agreed more closely with 
Anaspides than with the other two genera. From the position 
in which the fossils are preserved, it would appear that they 
followed a similar walking habit to Anaspides, and that the body 
was unflexed, 
DIVISION 2. PERACARIDA. 
The carapace, when present, leaves at least four of the 
thoracic somites distinct; the first thoracic segment is always 
fused with the head. The eyes are pedunculate or sessile. 
The mandible possesses a lacinia mobilis. A brood-pouch is 
formed in the female from oostegites attached to the thoracic 
limbs. The hepatic caeca are few and simple; the heart 1s 
elongated and tubular; the spermatozoa are filiform, and 
development takes place without a complicated metamorphosis. 
Order I. Mysidacea. 
The Mysidacea, although pelagic, are not very often met with 
in the true plankton on the surface; they generally swim some 
way below the surface, going down in many cases into the 
abysses. For this reason they thrive excellently in aquaria, and 
the common Mysis vulgaris is often present in such numbers in 
the tanks at the Zoological station at Naples as to damage the 
other inmates by the mere press of numbers. The Mysidacea, 
like the majority of the Peracarida, undergo a direct development, 
and hatch out with the structure of the adult fully formed. 
Many of the Mysidacea bear auditory sacs upon the sixth pair 
of pleopods, a characteristic not found in the Euphausiacea. 
Fam. 1. Eucopiidae.——The curious form Hucopia australis 
