MODERN SVSTtM. 



Class T. CRUSTACEA. 



Classification. — The Crustacea form two l;irf^e groii[)s or sub- 

 classes. The tirst of these, the j\Ialacostraca, liavc a pair of luaiulibles 

 and two pair of maxilkt bearing palpi, ami eight jiair of legs liirnished 

 with branchiae at their bases : all the genera that do not present the 

 above characters are referred to the artiticial assemblage denominated 

 Entomostraca. 



Subclass 1. Entomostraca — Legs branchial, or furnished with a]>- 

 pendages : mandibles wanting or generally simple : eyes sessile or pe- 

 dunculated. 



Subclass 2. Malacostraca. — Legs simple, without appendages : 

 viundibles \ alpigerous: eijes pedunculated or sessile. 



Subclass 1. E N T O ai O S T R A C A. ■ 



The animals of this subclass are but little known, and consequently 

 their arrangement is extremely imperfect. Some of the genera are pa- 

 rasitic, being found on the bodies of other animals, and some even un- 

 dergo transformation during their growth. 



The following arrangement is artiticial, but is well calculated to 

 enable the student to discover the Genera. 



Division I. — hoJy covered by a hoi'izontnl shield: eyes sessile. 



Subdivision 1. — Shell composed of hid one part. 

 * With jaus. 



Genus 1. APUS, Cuvicr, Latr., Leach. Apos, Scopoli. 



5Ae//crustaccous-membranaceous,orbiculate-ovate, behind deeply emar- 

 ginate: the back (with the exception of the anterior part) carinated: 

 eyes two, inserted at the anterior and middle part of the back ; some- 

 what prominent, slightly lunate, approaching each other, especially 

 anteriorly, where they touch each other : aiitennoi two, short, some- 

 what filiform, biarticulated, scarcely exserted, inserted behind the 

 mandibles : mandibnla two, corneous, somewhat cylindric, short, hol- 

 low within, points arcuated and compressed, the extreme apex straight 

 and very much denticulated : legs branchial and very nmnerous. 



The Api inhabit stagnant waters and ponds. 



Sp. 1. Ap. Montagui. Carina of the shell produced into a point behind : 

 anterior legs with articulated seta;: no lamella between the caudal 

 setffi. Encycl. Brit. Sup. i. Fl. '20. 



Inhabits England near Christchurch in Hampshire, where it was dis- 

 covered by Montagu, and was named allcr him by Leach. 



Apus pi-odudusol' Ldtrcille is synonymous wiUi thcLinncan Mono- 

 culus Apus. 



