68 



TWELFTH REPORT. 



A PRELIMINARY LIST OF THE CRUSTACEA OF MICHIGAN. 



A. S. PEARSE. 



It is not probable that this list contains nearly all the Crustacea 

 which occur in the State of Michigan. It is published at this time with 

 the hope that it niav prove of value as a summary of the present knowl- 

 edge of the carcinological fauna of the state, and that it may arouse 

 increased interest in this class of animals. The list has been largely 

 compiled from the publications at the end of this paper ; some species 

 have also been added from the writer's personal records. 



I had at first planned to publish keys to the genera and species, as 

 well as to the sub-classes, orders and sub-orders. This plan was given 

 up however, because the records for many of the orders were found to 

 show only a fraction of the species which probably occur in the state. 

 The following papers include keys by which the species of the various 

 orders mav be identified:^ 



Phyllopoda (1) 

 Cladoccra (37) 

 Ostracoda (1) 

 Copepoda (25) 



Aniphipoda (G) 

 Isopoda (G) 

 Mysidacea (1) 

 Decapoda (9) ; 



{'Sc 



)■ 



('95 ) 

 (:07),, 



-Packard 



-Herrick and Turner 

 -Sharpe (:03). 

 -Forbes ('97), Marsh 

 Wilson (:04). 

 -Weckel (:07).- 

 -Richardson ('05). 

 -Caiman (:09). 

 -Ortmann (:05), Pearse ( :10) 



Richard ('95). 



Schacht ('97, '98), 



KEY TO SUB-CLASSES. 



1. A variable number of body segments behind the head ; no gastric 



mill; larva usually leaves the egg as a free swimming nauplius 

 and passes through a metamorphosis; excretory organs are shell 

 glands Sub-class Entomostmca, p. 08. 



2. A definite number of segments behind the head (i. e. eight in thorax, 



seven in abdomen) ; gastric mill usually present; nauplius stage 

 usually passed through in the Qgg\ excretory- organs are an- 

 tennary glands Sub-class Malacostraca, p. G9. 



KEY TO ORDERS AND SUBORDERS OF EXTOMOSTRACA. 



1. Body distincth'^ segmented and covered by a cephalic carapace; post 

 cephalic a]>pendages leaf-like Order Plij/llopoda. p. G9. 



a. Phyllopoda of considerable size; with 10-60 pairs of leaf- 



like swimming feet Sub-order EiiplujUopoda, p. 69. 



b. Small Phyllopoda Avith compressed body inclosed in a bi- 

 valve carapace; four or five pairs of swimming feet; the 

 biramous autennal are the chief organs of locomotion. 



Sub-order Cladoccra. p. 69. 



^The numbers after each order and suborder indicate tlie number of species already 

 recorded from Michigan. Tlie list includes a total of eighty-six species and subspecies. 



