CRUSTACEANS. 237 



There is a great disparity in the size of specimens, some being twice 

 the dimensions, and their appearance very different from the aspect ot 

 others. 



Three specimens, none of them large, were taken ; a flat, round cake, 

 about a quarter of an incli in diameter, and nearly an eighth of an inch 

 thick, adhered to the under surface of one of them. — Plate LXIV. flg. 6 ; 

 of which the animal is seen enlarged, fig. 7. This, from its appearance, I 

 conjectured to consist of spawn, therefore it was transferred to a different 

 vessel, where it remained several weeks. At length, being divested of 

 the cake, I could not discover the presence of any portion of an ovarium. 



The animal survived nine months. 



Plate LXIV. 



Fig. 6. Pycnogonum Uttorale — The Whale Louse. 



7. The same, enlarged. 



8. Another specimen. 



9. Rostrum of the same, shewing the position of the black eyes, en- 



larged. 



Note. — Pycnogonum. — A promising young naturalist, Mr Henry 1). 

 S. Goodsir, enumerated several species of this genus among his earlier 

 observations. Being appointed Consei'vator of the Museum established 

 by the Edinburgh Royal College of Surgeons, he availed himself of all 

 opportunities of investigating the history of some of the lower animals 

 for several years, which he did with much success. His amiable disposi- 

 tion rendered him a universal favourite, and his talents always seemed 

 to me of the highest order. At length, being named naturalist and sur- 

 geon to the expedition under Sir John Franklin, to explore the Polar 

 seas, he accompanied it on its departure from Britain. 



§ 9. AsELLUS VULGARIS. — Plate LXV. figs. 1, 2, 3, 4, 5, 6. 



It is surprising, in viewing the British Fauna on a comprehensive 

 scale, how few of the Crustaceans, even of very moderate dimensions, 

 are to be found in the fresh-waters, though a sufficient number in form 



