ON A NEW GENUS OF COPEPOD CRUSTACEAN. 463 
On Obesiella lyonsielle, a new Genus of Copepod Crustacean. 
By W. G. Ripewoop, D.Sc., F.L.S. 
[Read 19th June, 1902.] 
THE specimens described in this paper were taken from the 
suprabranchial cavities of a single specimen of the deep-sea 
Lamellibranch Lyonsiella, dredged by the ‘ Challenger’ frem a 
depth of 1600 fathoms at Station 147 (off Crozet Is., W.N.W. 
of Kerguelen Is.). 
All the specimens were females.. Seven of them were perfect, 
but there were fragments of five more, so that there must have 
been twelve in the two suprabranchial cavities. They were so 
closely packed that the passage of water through the supra- 
branchial cavities must have been a matter of considerable 
difficulty. Five of the specimens remain preserved in alcohol, 
and these and the nine microscope-slides prepared from the 
others are in the Natural History Museum, London. The 
specimens measured 2°3 mm. in total length, and 1-4 mm. in 
maximum breadth across the thorax. 
Their most remarkable feature is the great inflation and loss 
of external segmentation of the thoracic region, and the reduc- 
tion in size of the thoracic appendages. The head has the 
appearance of being previded with a hood, owing to the presence 
of a dependent flap on each side. There are no eyes. Six pairs 
of cephalic appendages are present, and four thoracic. The 
abdomen is indistinctly divided into four segments, the last 
bearing a pair of caudal rami, short and papilliform, with four 
or five short sete. The mouth is extremely small, and set upon 
the pointed summit of an oral cone, into the conformation of the 
sides of which the third pair of appendages enter. 
The first pair of appendages (antenne) are of moderate size, 
flexible, and indistinctly segmented. The terminal fourth is 
rod-like, sometimes bent upon the rest of the limb, and ter- 
minated by a few short sete. 
The second appendages (second antenne) are slightly longer 
than the first. There are five segments, the proximal one being 
mostly concealed in a side view by the margin of the hood. 
The terminal joint is a strong curved claw. 
