ORDER ISOPODA. Ill 



with strong hooks. These are parasitic upon fishes. 

 Genera, Serolis, Cymothoa, IcJithyophilus, yEga, and 

 many other genera establislied by Dr. Leach, inchid- 

 ing the Limnoria terebrans, which is so destructive in 

 some of our ship-yards. 



3. Sphcpromidcc. — Antenute fom', abdomen with two arti- 



culations, swimmerets composed of two i)lates, the 

 lower being moveable. Genera, Zuzara, Splicer oma, 

 and other genera of Dr. Leach. 



4. IdoteidcB. — Antennae four, ])laccd on the same line, in- 



ternal small; abdomen with three articulations, desti- 

 tute of lateral swimmerets. Genera, Idotea, Steno- 

 soma, Arcturus. 



5. Asellidce. — Antenna? four, inserted in two lines ; abdo- 



men composed of a single articulation, \nthout lateral 

 swimmerets, and terminated by two long and slender 

 styles. Genera, Asellas, Oniscoda, &c. 



6. Oniscidce. — Internal antenna? almost ob- 



literated, abdomen six-jointed, with two 

 or four terminal appendages; some are 

 terrestrial. Genera, Ligia, Oniscus, Por- 

 cellio, Armadillo. 

 The most interesting insect in this order is 

 an extremely destructive little animal, forming 

 the genus Limnoria (Leach). The only species 

 is the Limnoria terebrans, which does not ex- '\""gfris° 

 ceed one-sixth of an inch in length, but which, 

 from its wood-eating habits and great powers of multiplica- 

 tion, is one of the most destructive of our insect enemies, 

 attacking piles of wood immersed in the water in our dock- 

 yards, flood-gates, timber bridges, chain piers, &c., and which 

 in a very short time it completely perforates in a most alarm- 

 ing manner, boring to the depth of several inches in every 

 threction. It is found in many parts of the coast, both of 



