ORDER PCECILOPODA • 
359 
the largest. Their body has no tail, and the testa forms only 
a plate, covering the anterior portion of the body. Their other 
organs are developed by degrees, in the course of successive 
moultings. M. Valenciennes, employed in the Museum of 
Natural History, has remarked that these animals were often 
devoured by the bird known vulgarly under the name of ivctg - 
tail . 
The known species being by no means numerous, it is not 
necessary to form, as Dr. Leach has done, with those which 
have a lamina between the filaments of the tail, a genus proper 
(Lepidurus). Such is the Monoculm apus y Linn. ; Schoeff. 
Monoc. vi. ; Limule serricaude , Herm. fils. ; Desm. Consid. 
lii. 2. The keel of the buckler is terminated posteriorly in 
a small spine, which is not seen in the following, Apus 
canciformis ( Binocle a queue en filet , Geoff. Insect, xxi. 4 ; 
Limulus palustris. Mull. ; Schoeff. Monoc. i.—v.; V Apus vert. 
Bose. ; Desm. ibid, li. 1.) ; the latter has no lamina between 
the filaments of the tail. It is the type of the genus apus 
proper of Dr. Leach. He has figured another species, Apus 
Moniagui, Edin. Encyc. Suppl. i. — xx. 
THE SECOND ORDER OF ENTOMOSTRACA, OR 
THE SEVENTH AND LAST OF THE CLASS 
CRUSTACEA. 
PCECILOPODA 
Is distinguished from the preceding by the diversity of form 
in the feet, the antenoi of which, of an indeterminate num* 
