i;6 ANNULOSA. 



mata and Podophthalmata, according as the eyes are sessile or 

 are supported upon eyestalks. 



DIVISION A. EDRIOPHTHALMATA. The division of the 

 Sessile-eyed Crustaceans comprises those Malacostraca in 

 which the eyes are not supported upon stalks or peduncles, 

 and there is mostly no carapace. The eyes are sometimes 

 compound, sometimes simple, and are placed on the sides of 

 the head. The head is almost always distinct from the body ; 

 and there are typically seven pairs of feet in the adult. 

 (Hence the name of Tetradecapoda applied to this division by 

 Agassiz.) The Edriophthalmata, include the orders Lizmodi- 

 poda, Amphipoda, and Isopoda, of which the two latter are 

 alone known in a fossil condition, whilst the last is the only 

 one of any importance. 



ORDER AMPHIPODA. 



Small Crustaceans in which the respiratory organs have the 

 form of membranous vesicles attached to the bases of the thoracic 

 limbs. Abdomen well developed, and composed of seven segments. 

 Seven pairs of thoracic limbs. 



The most familiar recent forms of the Amphipoda are the 

 "fresh-water Shrimps" (Gammarus), the Sand-hoppers (Tali- 

 trus), and the Shore-hoppers (Orchestid). The oldest repre- 

 sentative of the order is a doubtful form, which has been 

 described by Mr Woodward from the Upper Silurian Rocks 

 under the name of Necrogammarus. The Carboniferous genus 

 Gampsonyx has been referred here, but is more properly placed 

 amongst the Stomapoda. There are no other fossil Amphipods 

 of any importance. 



ORDER ISOPODA. 



Crustaceans in which the head is distinct from the segment 

 bearing tJie first pair of feet. The eyes are compound and sessile. 

 There are usually seven pairs of thoracic appendages, borne upon 

 seven movable segments. The animal sometimes /ins tJie power 

 of rolling into a ball. The abdominal segments are coalescent, 

 and form a broad caudal shield, beneath which the branchice are 

 carried. 



Of the living Isopods, some (Bopyridtz) are parasitic in 

 their adult condition upon other Crustaceans. Others, such as 

 the common Wood-lice (Oniscus), live habitually upon the land. 

 Others, again, are littoral in their habits, or frequent the sea. 



The oldest known Isopod is a large form which has been 

 described by Mr Henry Woodward from the Devonian Rocks 



