A72 MOLLUSCA. 
~ 
lateral border, somewhat like a natatory membrane. Head not more 
than one-third as wide as the body ; eyes prominent, of medium size, 
the iris blue-black, the pupil silvery green, surrounded by light brown 
lids. Aperture extending to the eyes; natatory tube short and small, 
bulbous at base, truncate at tip. Mouth rather large; beaks black ; arms 
very large at their base, and gradually tapering. Umbrella very large, 
the membrane passing to the very tip of each arm, along the edge 
most distant from the dorsal median line; the contiguous faces of the 
dorsal pair are therefore destitute of a membrane, except at the base, 
while the contiguous faces of the lower pair are furnished with them. 
Cupules crowded and alternating, short, on a broad-based, constricted 
peduncle, the termination divided into segments by radiating furrows, 
and these again subdivided by finer lines of a milk-white colour, some- 
what ochreous at centre. They are very large, some of them being 
an inch and a quarter in diameter. Colour on the back dark choco- 
late, delicately marked with streaks of ashy white; belly much paler; 
inside of arms bluish-white. 
Length of body to the opening on the belly, 5-2 inches; length to 
the eyes, 7-5 inches; breadth of head, 27 inches; circumference of 
body at the largest part, 11-2 inches; length of arms from the base, 34 
inches; circumference of arms at the largest part, 3-1 inches; diameter 
of the largest cupule, 1:3 inches; length of tube, 15 inches; breadth 
of umbrella, 8 inches; total length, 43 inches. 
Found by Lieutenant Alden, near the shore in Orange Harbour, 
in the vicinity of the observing station. 
This very large species is remarkable for the magnitude of its um- 
brella and its cupules, but especially for the narrow membrane extend- 
ing along the sides of the body, which has not been noted as belonging 
to any other species except O. membranaceus, Quoy. It is closely 
allied to O. Fontainianus, D’Orb., so remarkable for the cluster of four 
or five large cupules near the bases of the lateral arms, while all the 
others are very much smaller. O. tehuelcha, comes from the same 
region, and has something of the same general characters; but the 
comparative size of the head and the umbrella is quite different, the 
membrane along the arms being entirely wanting. ‘The description 
is mostly made from notes by Mr. Couthouy, whose name I adopt. 
Figure 586, 586 a, two views of the animal, reduced, with details. 
