530 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvm. 



SYSTEMATIC. 

 HISTORICAL. 



The first which can really be called a classification of the parasitic 

 copepods was made by Burmeister in 1833 and included only 23 out of 

 the 80 and more genera known at the present day. 



The group was divided into families on the basis of the presence 

 and structure of the antenna? and segmented feet. 



Each family was divided into genera upon a different basis, that for 

 the Caligidre consisting in the presence or absence of eyes and the 

 structure of the fourth thoracic feet. 



The next important classification was by Milne Edwards in his great 

 work on the Crustacea in 1840. He raised the number of genera of 

 these parasites to 35 and divided them first according to the fusion of 

 the head and thorax, and the structure of the antennae. They were 

 then subdivided by the presence or absence of dorsal plates on the 

 free thoracic segments, while the Caligidas were classified hj the 

 structure of the fourth legs. This resulted in throwing all the forms 

 with dorsal plates on the thorax into the Pandarina?, irrespective of 

 their relations in other particulars. 



As there were only 9 genera known at that time in the Caligida?, 2 

 of which, Chalimus and JVogagtis, were spurious, such a division 

 answered well enough, and it located each genus just where it stands 

 at the present time. 



A third classification was published by Steenstrup and Liitken in 

 1861, and by Nordmann in 1861, the two being identical. 



Thejr increase the number of genera to 68, of which 20 belong to 

 the Caligidaa; they divide them first according to the structure of the 

 egg sacks and the arrangement of the eggs. 



The second subdivision is on the basis of the degree of fusion 

 between the head and thorax, and on the presence or absence of a 

 carapace. In the family Caligidse the classification is based on the 

 structure of the fourth feet, the presence of dorsal plates on the free 

 segments of the thorax, and the presence of lunules on the frontal 

 plates. 



Heller, in 1865, adopted practically the same classification, but gave 

 a much more elaborate analysis of the genera belonging to the Cali- 

 gidae, which he increased to 26 in number. 



For this analysis he makes use of (1) the structure of the rostrum 

 and "palps" (second maxilla?); (2) the degree of fusion between the 

 head and thorax; (3) the presence of dorsal plates on the free thorax 

 segments; (4) the presence of lunules; (5) the structure of the fourth 

 thoracic feet. 



In the following year, 1866, there appeared the first number of 

 Bronn's Thierreich, in the fifth volume of which, under the Copepoda, 



