CRUSTACEANS. 227 



each side of the head. The usual colour of the animal is dingy white 

 throughout. 



The four pair of upper members resemble a rich furred ruff, in fine 

 specimens ; but, in poor specimens, the fringe clothing them is little 

 more than perceptible, — if these ai'e to be accounted limbs, the whole 

 complement, including the six posterior members, is fourteen, which may 

 have led some observers to consider the Astacilla a species of Oniscus. 



Its motions are very singular, aggravated, perhaps, by apparent ex- 

 traordinary disproportions. The position frequently assumed, and long 

 retained, is adhering by the hind legs to any foreign substance, with the 

 head downwards. I have never seen any specimen attempt to swim, to 

 which, indeed, its general form is quite adverse. 



Plate LXIII. 



Figs. 1, 2. Astacilla, natural size, fig. 10, enlarged. 



The exuviation of a specimen took place during the first week of 

 October, when the shell was detached in two portions, the posterior com- 

 prehending the six hind limbs. 



The season of propagation extends from March to December. The 

 union of two fine large specimens seemed to ensue on the 12th of this 

 latter month : ova appeared June 14th, on the thorax and abdomen of 

 another specimen. But the presence of a diminutive white zoophyte 

 injured the roe, which proved abortive of progeny. 



As the position of the spawn is not exposed to view it certainly re- 

 mains attached to the parent, while the young quit the capsules, and are 

 seen running about the vessel. 



A full grown specimen having reached me on March 21, a suitable 

 vessel received it. Herein I was much surprised next day to find above 

 sixty young, which had been recently produced. All were pure white ; 

 they exceeded a line in lengih ; their black eyes were rather oval ; and 

 they entirely resembled the form of the parent. 



Some circumstances are perplexing, especially regarding the number, 

 for it may be questioned whether some had not been concealed, or at- 

 tached unobserved. 



