Dr. LeAcn's Arrangement of the Crustacea, $c. 387 
Classis III. ARACHNIDES. 
From this class I have not only removed the Tetracera and 
Myriapoda of Latreille as before mentioned, but also the Parasita 
and Thysanoura of the same author, which consist of genuine 
Insects; and to the Aracunipzs I have added the genus 
Nycteribia, which agrees with them in general structure. 
Subclassis I. CEPHALOSTOMATA. 
Os frontale ad caput adnexum. (Pedes octo aut sex.) 
* Pedes coxis, femoribus, tibus tarsisque formá distinctis. 
Ordo I. PopvosomatTa. 
Corpus 4-articulatum, et quasi e coxarum junctione efformatum. 
Os tubulosum. Oculi quatuor tuberculo impositi. Pedes octo. 
Ordo Il. PoLYMEROSOMATA. 
Corpus e serie segmentorum efformatum, abdomine haud pedun- 
culato. Os mandibulis didactylis et maxillis instructum. Oculi 
duo, quatuor, sex aut octo. Pedes octo. 
Gas IH. DIMEROSOMATA. 
Corpus e segmentis duobus efformatum, abdomine pedunculato. 
Os mandibulis et maxillis armatum. Oculi sex aut octo. Pedes 
octo. : 
VOL. XI. A EEE : ** Pedes 
