ORDER ISOPODA — ASELLUS. 49 



This apparently insignificant and minute animal is capable of great injury to wood exposed 

 to salt water. It attacks in countless numbers the piers of bridges, wooden wharves, and all 

 submerged timber, piercing it in every direction, and soon rendering it useless. It has been 

 computed that a stick of timber exposed to these animals, where they are abundant, will lose 

 an inch of its diameter annually. They act chiefly below low-water mark. The best mode 

 of protection yet discovered is a coat of verdigris, or of metallic copper. The same purpose 

 is effected by covering the whole surface with broad-headed copper nails. This animal 

 attacks in preference pine and other soft woods, although none, except perhaps live oak, is 

 exempted from its ravages. Its injuries are very partially counterbalanced by its benefits in 

 destroying sunken timber, or vessels, which might obstruct channels or tideways. 



GENUS ASELLUS. Geoffroy. 



Body oblong, depressed. Head distinct. Segments transverse, crustaceous. Tail of a single 

 segment, with two bifid appendices. Feet fourteen. Four apparent antenna?, setaceous, 

 unequal ; the two superior much shorter, four-jointed ; the two lower much longer, of five 

 joints. Several pairs of jaws. Eyes two, simple, sessile. 



ASELLUS COMMUNIS. 



Ascllus communis. Say, Journ. Acad. Nat. Sciences, Vol. 1, p. 427. 



Description. Segments transverse, subequal, indistinctly emarginate on the lateral edges, 

 furnished with short rigid hairs. Head narrower than the first segment, and not longer. Eyes 

 obovate, oblique, black, prominent. Inferior antennae equal to the peduncle of the superior 

 ones, which latter extend to the base of the tail. Tail as broad as the segments of the body, 

 and equal to the two preceding ones united. Appendices as long as the tail ; laciniae sub- 

 equal, peduncle dilated. Anterior feet monodactyle, unarmed ; thumb as long as the hand. 

 Hand oval ; carpus triangular, remaining gradually longer to the hind pair. 



Length, 0.25. Breadth, 0-09. 



This is a very common species in our freshwater streams, and usually found under stones 

 and bits of wood. The female is distinguished by a valvular follicle beneath, covering the 

 young. 



Fauna — Part 6*. 7 



