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DR BAIRD ON ENT0M08TRACA. 146 



Arrangement of the British Entomostraca, ivith a List of Species^ 

 particularly/ noticing those which have as yet been discovered 

 within the bounds of the Club. By Williah Baird, M.D., 6mj. 



Sub-Kingdom, Annulosa. 

 Class, Crustacea ; Division, Entomostbaoa. 



The Entomostraca may be characterized by their being all aqna- 

 tic, — by their being either covered with a shell, which is of a homy 

 or coriaceous texture, and formed of one or two pieces, in some 

 approaching in appearance to a bivalve shell, in others, being in 

 the form of a buckler, which completely, or in part, envelopes the 

 body of the animal ; or being completely enclosed in a hard testa- 

 ceous covering of several pieces, — ^by having branchiae attached 

 either to the feet or organs of mastication, — ^by their feet being 

 jointed, and all more or less ciliated, — and by their undergoing a 

 regular moulting or change of shell as they grow, in some ap- 

 proaching to a species of transformation. 



Legion 1st. — BrANCHIOPODA — Latreille, 

 Mouth furnished with organs fitted for mastication. Branchiae at- 

 tached to the feet or jaws. Body sometimes naked, but generally 

 having an envelope, in form of a buckler, enclosing the head and 

 tliorax, or in the shape of a bivalve shell enclosing the whole 

 animal. Feet varying in number, all articulated and more or less 

 ciliated. Antennae two or four, articulated, and generally ciliated. 

 Eyes sometimes two or even three, but most frequently only one, 

 or if more, so closely approximated as to appear single. They are 

 all free and unattached, swimming at large in the water, or creep- 

 ing on aquatic plants. 



Legion 2d. — P^CILOPODA — Latreille. 

 Mouth not possessed of organs fitted for mastication, having in- 

 stead an apparatus adapted for sucking. Feet partly formed for 

 walking or prehension, and part branchiferous, and fitted for swim- 

 ming. Body, in the greater number, enclosed almost totally within 

 a buckler, consisting generally of one piece, more seldom of two. 

 Parasitical upon fishes, &c. 



