IDOTEA PELAGICA. 385 
tion (No. 607a). It is certainly very closely allied to 
I. tricuspidata. The body is covered with minute dots; 
the lower antennz are about one-fourth of the entire 
length of the animal; the sides of the segments of the 
body have the epimeral or coxal articulations as in J. 
tricuspidata, and the basal segments of the tail are arti- 
culated in the same manner as in that species, the union 
between the third and fourth segments at the sides being, 
however, more decided than in J. fricuspidata. The 
slight central keel at the end of this segment appears to 
be the most important character. 
Common on the Bell Rock in the Frith of Forth. 
There are also specimens in the British Museum com- 
municated by Col. Montagu. Specimens occur in Mr. 
Thompson’s Irish Collection, taken at Belfast Bay in 
March, 1841, one about a sixth of an inch in length, as 
well as another, a quarter of an inch long, from the 
stomach of a sheldrake, shot at the end of December, 
also in Belfast Bay. It is also contained in Humphrey’s 
‘Contributions to the Fauna of the Co. Cork,” and we 
have received it from the Eddystone Lighthouse. It is 
probably common all round the coast in the laminarian 
zone. 
VOL. II. Cc 
