78 MODEKM S\;5T£M. 



Class I. CRUSTACEA. 



CLASSirrrATiox. — The Crustacea form two large groups or sub- 

 classes. The tirst of these, the Mulacostraca, have a pair of mandibles 

 and two pair of maxilke bearing palpi, and eight pair of legs furnished 

 with brauchiLe 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 ap- 

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

 dunculated. 



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

 viandibles j alpigerous : eyes pedunculated or sessile. 



Subclass 1. ENTOMOSTRACA." 



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

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

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

 dergo transtbrmation during their growth. 



The following arrangement is artificial, but is well calculated to 

 enable the student to discover the Genera. 



Division I.— Body covered hi/ a horizmital shield : eyes sessile. 



Subdivision 1. — Shell composed of but one part. 

 * 117/7* jaws. 



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



<S'Ae//crustaceous-membranaceous,orbiculate-ovate, behind deeply emar- 

 ginate: the buck (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 : antemus 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 denticiUated : legs branchial and very numerous. 



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 

 setae. Encycl. Brit. Sup. i. Fl. 20. 



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

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



Apus productus of Latrcille is synonymous witU the Linnean Mono- 

 cuius Apus, 



