INTRODUCTION. 



Ihe Cumacea form a sharply-defined and very peculiar group of Crustacea, 

 the systematic position of which has been much debated among zoologists, most 

 of the earlier authors referring them to the lower Decapods, whereas in recent 

 time they have generally been placed close to the Isopoda. The fact is that they 

 (lifter materially from both of these groups, and should thus more properly be consi- 

 dered as constituting a distinct order, occupying its place between the great divisions 

 Podophthalmia and Edriophthalmia. It is true, inded, as first shown by Dr. Dohrn, 

 that the embryonal development of the Cumacea agrees very nearly with that of the 

 Isopoda; but in all other respects these Crustacea exhibit, in my opinion, a much 

 closer relationship to the Podophthalmia than to the Isopoda. Among the former, 

 it is chiefly the Schizopoda with which the Cumacea have many features in com- 

 mon, though the external appearance is certainly very different; and even 

 those anatomical characters which have been specially adduced as proofs of 

 the near relationship of the Cumacea with the cheliferous Isopoda, viz., the pre- 

 sence of a reflexed palp on the anterior maxilla?, and the peculiar development 

 of the epipodite on the 1st pair of maxillipeds, may be found quite as distinct 

 in some of the Schizopoda, e. g. Gnathophausia. In my opinion, therefore, 

 the recent arrangement of the Cumacea as a sub-order of the Edriophtiialmia can 

 scarcely be supported. On the other hand, I consider that the differences from the 

 Schizopoda are still great enough to forbid of the Cumacea being included in the 

 great division Podophthalmia. 



Our knowledge of these singular Crustacea does not date from very 

 long ago. The first form recorded is probably that described by Lepechin in the 

 year 1780, as Oniscus scorpioides, which has turned out to be a species of the 

 genus Diastylis. Another Cumacean form was observed in the year 1804 by 

 Colonel Montagu, and designated by the very same specific name; but this 

 author erroneously believed that the solitary specimen found was a defective 



1 Crustacea. 



