a Genus of Entomostraca new to Great Britain. 413 



habits^ and of the animal rolling itself in the mud, as well as 

 owing to the pilose covering of the shell, that it owes the coating 

 of mud. Diatoms, and Desmids which render it so difficult a 

 a matter to see the structure of the organs of the body contained 

 within the carapace. That the coating of extraneous matter is 

 the effect, and not the cause, of the inability of the animal to 

 s^nm is proved by the fact that one of the specimens obtained, 

 which was sent to Mr. G. S. Brady for the purpose of obtaining 

 his kindly extended and valuable aid in the dehneation of the 

 species, gave birth to five young while in his possession ; and he 

 informed us that, though these young, when first born, were able 

 to raise themselves shghtly in the water, yet it was not more 

 than about half an inch, nor could this be effected without great 

 effort, or, apparently, without the assistance of the sides of the 

 vessel in which they were contained ; and when two or three 

 days old, even this limited power of locomotion was lost. Mr. 

 Brady wrote to us the following vivid description of the motions 

 of these young specimens : — " It is a sight to see the brutes 

 swim, or tnj to swim, under the microscope. "When a good view 

 from the dorsal aspect is obtained, one sees that they put their 

 two great antennae together, and strike out in a good bold sweep 

 like any Christian, the superior antennae working synchronously, 

 but in a smaller arc, inside the greater ones. The motion of 

 these lesser antennse is very beautiful ; and the muscular con- 

 tractions in the basal joints of the greater ones are remarkably 

 plain, throwing the limb into great wrinkles. "When the animal 

 is tired of this sort of exertion, it stops its arms, and begins 

 working its branchial apparatus at a great rate ; but, so far as I 

 can see, the two systems are never in active motion together. 

 They seem to attract dust and parasitic gi-owths; for, though 

 kept in simple water, they are surrounded with confervoid fila- 

 ments. Diatoms, Oscillatorise, &c." 



Another remarkable feature in the history of this Daphnian 

 is the great scarcity of the species individually. As a rule, where 

 an Entomostracan occurs at all, it is to be met with in abund- 

 ance. This is very far from being the case with A. sordida. 

 Failing in the attempt to make out the structure of the three 

 specimens we had obtained in the Bishop-Middleham colliery 

 pond, and being unwilling to destroy them by attempted dissec- 

 tion, we hoped to render the dense character of the carapace- 

 valves more transparent by mounting them in Dean's medium. 

 The result was far from satisfactory. The pond was therefore 

 revisited in the hope of again finding the species, and this not 

 once, but many times ; but, though the greatest trouble and 

 care were taken, no further specimens could be met with. Sub- 

 sequently, however, a single example was obtained under pre- 



