I I 8 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 

 (Gamysonyx, Pcdaeocaris, 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 ; tlie first thoracic segment is always 

 fused with the head. The eyes are pedunculate or sessile. 



The mandible possesses a lacinia mobilis. A brood-puuch is 

 formed in tlie female from oostegites attached to the thoracic 

 limbs. The hepatic caeca are few and simple ; the heart is 

 elongated and tubular : tlie 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 vidgaris 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 tln^ Mysidacea bear auditory sacs upon' the sixth pair 

 of pleopods, a characteristic not found in the Euphausiacea. 



Fam. 1. Eucopiidae. — The curious form JSucopia australis 



