GENERA CUMA, ALAUNA, AND I30D0TIUA. 325 



" The branchiae are situated on each side of the thoro,x, imme- 

 diately above the insertions of the legs, and approach^ in their 

 comb-like appearance, to those of the higher Crustacea. Interiorly, 

 each of them is connected with the superior foot-jaws, and, except- 

 ing that connection, lies apparently quite free in a sac formed by 

 the reflection of a thin transparent membrane, which lines the 

 internal surface of the thorax. The superior part of the branchiic 

 consists of one continuous piece, which is bent in a hook-like man- 

 ner at its posterior extremity ; the branchiae themselves arise from 

 the inferior edge of this part, and are about sixteen or seventeen 

 in number ; they are not laminated like those of the higher Crus- 

 tacea, but consist of one large piece, which is apparently composed 

 of a great number of cells. 



" The organs of generation are not apparent in the male, but in 

 the female, and, especially when she is loaded with spawn, these 

 organs are at once perceptible. They are very similar in their 

 structure and appearance to the same parts in the female Mysis, 

 They consist of four scales, which arise from the inferior edge of 

 the thoracic segments. These scales are of an irregular oval shape, 

 concave internally, and convex externally, and they are overlapped 

 by one another. The eggs are of considerable size, and of a bright 

 straw colour. It is from the genus Ciima only that these obser- 

 vations were taken in regard to the organs of generation. 



" When a portion of the skin, or shell rather, is placed under the 

 microscope, it presents a very beautiful appearance ; it apparently 

 consists of a great number of nuclei, arranged in some degree of 

 order. These nuclei are stellated, and here and there larger nuclei 

 may be observed, the edges of which are quite smooth. 



" The structure of these animals is so peculiar, as to render the 

 assignation (at present) of a proper place in a natural arrangement 

 of the class, a point of very considerable difficulty. This arises in 

 a great measure, without doubt, from our very limited knowledge 

 of the class. I rather think, however, that they should be ranged 

 among the lower Decapoda macroura. 



