Dr. Leach's Arrangement of the Crustacea, ^c. 
387 
Classis III. A R A C H N I D E S. 
From this class I have not only removed the Tetracera and 
Myriapoda of Latreille as before mentioned, but also i\\e l^arasita 
and Thysanoura of the same author, which consist of genuine 
Insects ; and to the Araciinides 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, tibiis tarsisque forma distinctis. 
Ordo I. PoDOSOMATA. 
Corpus 4-articulatum, et quasi e coxarum junctione efformatum. 
Os tubulosum. Oculi quatuor tuberculo impositi. Pedes octo. 
Ordo II. P OLYMEHOSOMATA. 
Corpus e serie segmentorum elForraatum, abdomine baud pedun- 
culato. Os mandibulis didactylis et maxillis instructum. Oculi 
duo, quatuor, sex aut octo. Pedes octo. 
Ordo III. Dimeeosom ATA. 
Corpus e segmentis duobus elformatum, abdomine pedunculato. 
Os mandibulis et maxillis arrnatum. Oculi sex aut octo. Pedes 
octo. 
3 E 
VOL. XI. 
** Pedes 
