ORDER ISOPODA. Ill 



\vith strong hooks. These are parasitic upon fishes. 

 Genera, Serolis, Cymothoa, Ichthyophilus, JEga, and 

 many other genera established by Dr. Leach, includ- 

 ing the Limnoria terebrans, which is so destructive in 

 some of our ship-yards. 



3. Sphceromida;. Antenna; four, abdomen with two arti- 

 culations, swimmerets composed of two plates, the 

 lower being moveable. Genera, Zuzara, Sphceroma, 

 and other genera of Dr. Leach. 



-1. IdoteidcE. Antennae four, placed on the same line, in- 

 ternal small; abdomen with three articulations, desti- 

 tute of lateral swimmerets. Genera, Idotea, Steno- 

 soma, Arcturus. 



5. Asellida. Antennae four, inserted in two lines ; abdo- 

 men composed of a single articulation, without lateral 

 swimmerets, and terminated by two long and slender 

 styles. Genera, Asellus, Oniscoda, &c. 

 f>. Oniscidce. Internal antennae 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- 

 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 

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



