J.ERA NORDMANNI. 321 



ingly removed it therefrom, and formed for its reception 

 a new genus, Jaridina, in consequence of the branchial 

 apparatus on the underside of the tail not being covered 

 by a " grande lame operculaire qui chez eux remplace les 

 premieres fausses pates " (which had been given as the 

 generic distinction between Asellus and Jcera). Having, 

 however, ascertained that this "grande lame" is a sexual 

 distinction peculiar to the females, we are under the 

 necessity of referring the new species to the genus Jaera, 

 with which it agrees in all its essential characters. 



It is considerably broader than J. albifrous, the lateral 

 margins being very thin and dilated, as well as ciliated 

 with rather strong bristles set on at right angles, a 

 peculiarity of structure eminently fitted for enabling the 

 animal to reside in flat crevices, beneath stones, &c., in 

 situations often uncovered by the tide ; the ciliation of 

 the sides of the body serving for the retention of the 

 fluid which supplies the material for respiration ; just 

 as in many insects residing in occasionally submerged 

 situations under stones, it maintains a supply of air for 

 the like purpose. The head is deeply incised in front, 

 for the reception of the antennee, the inner pair of 

 which are very short, and four-jointed, the terminal joint 

 offering no apparent trace of articulation ; the outer 

 antennae are not more than one-third of the length of 

 the animal, the third joint being only about twice the 

 length of the preceding, and not half as long as the 

 following joints, the flagellum is very slender and multi- 

 articulate. The terminal segment, or tail, is large and 

 semicircular, with a rather deep semicircular incision 

 at its extremity, within which are affixed the two caudal 

 appendages, consisting of a small oblong basal joint, at 

 the extremity of which are attached two small scales, 

 the outer one being extremely minute and conical, the 



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