On the AstacilldB of Cordiner, 109 



nor other appendage," in reality possesses a pair of natatory 

 feet. These, however, having their origin very near to the 

 anterior margin of the segment, may, on a cursory view, be 

 regarded as in connexion with the antecedent segment — a de- 

 ceptive appearance, which, in the present instance, has misled. 

 In consequence of this mistake, the first pair of feet are as- 

 signed to the head, though they belong to the first segment of 

 the body. In the specimen now before me, the inferior 

 antennae, instead of having only seven joints, as represented by 

 EXr. Johnston in his description, possess eight, the three last 

 appearing to constitute a single segment. 



Among the marine productions collected during Captain 

 Parry's first voyage to the Arctic Seas, and noticed in the Ap- 

 pendix which was published in 1824, a crustaceous animal 

 is described and figured by Captain Sabine, under the name 

 of Idotea Baffini, as brought up by the trawl in considerable 

 numbers from twenty fathoms depth, coarse sandy bottom, on 

 the west coast of Baffin's Bay, in latitude 71°. The propriety 

 of inserting this species along with the Idoteae could only have 

 been justified, in consequence of the resolution of the author 

 to follow the system of Lamarck, in which the genus Idotea is 

 characterised in such general terms, as to admit animals differ- 

 ing widely in structure from the typical species, as in the pre- 

 sent iristance. The same animal is retained in the genus Idotea 

 by Lieutenant J. C. Ross, in the appendix to Captain Parry's 

 Third Voyage, p. 117. 



The general connexion between the Astacilla and Idotea 

 Baffini occurred to me at once, on comparing the very expres- 

 sive delineations which Mr. Cordiner has given of the one, and 

 Mr. Curtis of the other; and their generical connexion was 

 ascertained without difficulty, by comparing together specimens 

 of each. The example of the Arctic animal in my possession 

 was much infested with the campanularia volubilis. It dif- 

 fers chiefly from Cordiner's animal in the greater number of 

 segments in the last joint of the under antennae, and the greater 

 brevity of the fourth segment of the body. 



Viewing all these circumstances in connexion, I was dis- 

 posed to consider the Astacilla (assuming the name employed 

 by Cordiner, from its priority) as a well-marked genus in the 

 family iDOTEADiE, and sufficiently distinguished from Idotea 



