Nov, 1907.] THE VICTORIAN NATURALIST. 117 



DESCRIPTION OF A NKW REMARKABLE CRUS- 

 TACEAN WITH PRIMITIVE MALACOSTRACAN 

 CHARACTERS. 



Bv O. A. Sayce. 



{Read be/ore the Field Naturalists' Club of Victoria, Sth October, 1907.) 



Thr new crustacean, of which I now offer a preliminary descrip- 

 tion, is a very important one, Iiaving in a major degree the 

 characters of the stalked-eyed forms, although possessing definitely 

 sessile eyes, and also bearing other features which shed additional 

 light on divergent groups. I consider it the most primitive 

 sessile-eyed Malacostraca hitherto recorded. Its nearest ally is 

 undoubtedly the stalk-eyed Annspides tnsmnnice, G. M. Thomson. 



It has been easy to separate crustaceans, apart from the more 

 primitive forms, such as the Entomostraca, into two divisions — 

 one, possessing movably stalked eyes, Podophthalma, and another, 

 with sessile eyes, Edriophthalma— and hitherto there has been no 

 sharp merging of one into the otlier. This basis for classification 

 was adopted by Leach in 1815, and is to-day the generally 

 accepted one. 



For some years past, however, some few carcinologists, notably 

 Prof. Boas, and later Dr. H. J. Hansen, have conceived that in 

 certain circumstances this is not a natural classification, and that 

 in the more primitive forms of each division — viz., the stalk-eyed 

 Schizopoda and the sessile-eyed Isopoda — some of the former are 

 more closely related to the latter than are some Schizopod families 

 to each other. Hansen differs in many points from Boas, and no 

 subsequent writer seems to have adopted their recommendations 

 until recently, when Dr. W. T. Caiman* has conformed to Han- 

 sen's suggestion (with some modifications and additions), and done 

 away with the Schizopoda as a natural group, uniting some, the 

 Euphausidacea, to the Decapoda (crayfish, crabs, &c.), and the 

 remainder, the Mysidacea, to a large group including all the 

 sessile-eyed forms (Isopoda and Amphipoda). 



This is not the place to enter into a detailed discussion as to 

 the systematic position of the present species, but I shall do so in 

 another place, and give a detailed description, with illustrations 

 of its anatomy. Sufficient to say here that it cannot be placed in 

 Caiman's division Syncarida, composed of the single order 

 Anaspidacea, to which the present species is rather closely allied, 

 without considerable alteration of his diagnosis ; for instance, it 

 has not all the thoracic somites distinct, the anterior one being 

 coalesced with the head, the eyes are not pedunculated, nor are 

 the thoracic limbs flexed between the fifth and sixth joints, but 

 between the fourth and fifth. I can, however, respect his order 

 Anaspidacea, so far undefined, and in consequence of the present 

 species I offer a diagnosis of it. 



* On the Classification of the Crustacea : Malacostraca, By W. T. Caiman. 

 D.Sc, Ann, & Mag. N. Hist. (7), xiii., p. 144 (1904). 



