78 
MODERN SYSTEM. 
Class I. CRUSTACEA. 
Classification.' — The Crustacea form two large groups or sub- 
classes. The first of these, the Malacostraca, have a pair of mandibles 
and two pair of maxilla; bearing palpi, and eight pair of legs furnished 
with branchia; at their bases: all the genera that do not present the 
above characters arc referred to the artificial assemblage denominated 
Entomosttaca. 
Subclass 1. Entomostuaca — Leg* branchial, or furnished with ap- 
pendages : mandibles wanting or generally simple : eyes sessile or pe- 
dunculated. 
Subclass 2. Malacostraca. — Legs simple, without appendages; 
mandibles palpigerous: eyes pedunculated or sessile. 
Subclass 1. EN T O M O S T It A C A. ' 
The animals of this subclass are but little known, and consequently 
their arrangement is extremely imperfect. Some of the genera arc pa- 
rasitic, being found on the bodies of other animals, and some even un- 
dergo transformation during their growth. 
The following arrangement is artificial, but is well calculated to 
enable the student to discover the Genera. 
Division I . — Body covered by a horizontal shield: eyes sessile. 
Subdivision 1. — S hell composed of but one part. 
* With jam. 
Genus 1. A PUS, Cuvier, Latr., Leach. Aros, Scopoli. 
SZ/eMcruslaccous-meinbranaceotis, 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, especial),' 
anteriorly, where they touch each other: antenna two, short, some- 
what filiform, biarticulated, scarcely exserted, inserted behind the 
mandibles: mmdibulte two, corneous, somewhat cylindric, short, hoh 
low wil bin, poi nts arcuated and compressed, the extreme apex straigh 1 
and very much denticulated: legs branchial and very numerous. 
The Api inhabit stagnant waters and ponds. 
Sp. 1. Ap. Monhtgui. Carina of the shell produced into a point behind- 
anterior legs with articulated seta;: no lamella between the caud®* 
seta:. Encycl. Brit. Sup. i .Pi. 20. 
Inhabits England near Christchurch in Hampshire, where it was di s ' 
covered by Montagu, and was named after him by Leach. 
Apus product us of Latreille is synonymous with the Linncan 
ealus Apus. 
