Decapod (Astacus) that had lost its head. In the year 1828, H. Milne-Edwards 

 observed apparently the same form, and established for its reception the genus 

 Cuma; and it is from this genus that the name of the whole order is derived. 

 Another genus, however, viz. that of Diastylis, is, in fact, of a still earlier date, 

 having been established by the American zoologist Say, in the year 1818. It is 

 rather strange that the founder of the typical genus Cuma, H. Milne-Edwards, 

 subsequently altogether abandoned this genus, believing the form upon which it 

 was founded to be only a larval form of some higher Crustacean ; and this er- 

 roneous assumption was entertained by many other authors, according to whom 

 the Cumacea should be wholly discarded from the zoological system, as only re- 

 presenting immature animals. Certainly both Kroyer and Goodsir. in the year 

 1841, clearly showed the Cumacea to be perfect animals, and added several new 

 species; but there was still for many years doubt among zoologists as to the 

 true nature of these Crustacea. Thus Dana, in his great work on Crustacea, did 

 not include the Cumacea at all in his carcinological system, urging in support of this 

 action a statement given in 1852 by the celebrated Prof. L. Agassiz, who claimed to 

 have witnessed the escape of true Cumacea from the ova of Hippolyte and other Carids. 

 Meanwhile the investigation of these problematical Crustacea was continued by 

 several distinguished zoologists, Kroyer, Sp. Bate, and Prof. Lilljeborg, and all of 

 them agreed in absolutely denying the larval nature of the Cumacea, giving most 

 convincing reasons for their opinion. Notwithstanding this, even in the year 1858, 

 the Cumacea were declared by a high authority, Prof. H. Milne-Edwards, to be 

 immature animals, and were placed in the same rank as Phyllosoma, Erichtiis, 

 Zoea and other larval forms. 



As will appear from the above short historical account, the general ack- 

 nowledgement of the Cumacea as perfect animals worthy of being ranked in the 

 carcinological system, is of comparatively recent date. The number of species at 

 first detected was a very limited one, and they were generally all referred to a 

 single genus, Citma. Subsequently, a few additional genera were established, but 

 some of these have turned out to be spurious, being founded only on the male sex. 

 Sp. Bate comprised all the genera at that time established, within a single family, 

 that of the Diastylidw, which he believed to be nearly allied to the Stomatopoda. 

 In recent times, by the investigation of several zoologists, the number of both 

 species and genera has considerably increased, and it accordingly appeared very 

 desirable to group together the several genera in a suitable manner, by a sub- 

 division of the original family. The first attempt to effect such a classification 

 was made in the year 1879 by the present author, who, in his account of the 

 Mediterranean Cumacea, arranged the 18 genera at that time known, in 8 distinct 



