CEPHALOPODA. 471 
between the annulations and dots, a brilliant silvery lustre, with a 
greenish play of colour; after remaining in spirits, it dries of a slaty 
hue, on which the brown dots are still apparent. 
Whole length about six inches; length of sac above, two and three- 
fourths inches; below, two and a half inches; breadth one and a half 
inches; length of siphon one and three-fourths inches; length of supe- 
rior arms five inches; of inferior arms four and a half inches; superior 
lateral, six inches; inferior lateral, four inches; diameter of umbrella 
from side to side an inch and a quarter; vertical, one and three-fourths 
inches. 
Taken in a seine near the Sugar Loaf, Rio Janeiro, and its colour 
described by Mr. Couthouy during life. 
The sHexu belonging to this animal is not known. No impressions 
existed on its surface, answering to the folds of a shell, so that it had 
not very recently, if ever, occupied one; it is conjectured that the 
shell is formed by the female, for the protection of her eggs during 
nidification. The animaL resembles most nearly A. argo, especially 
the one figured by Férussac and D’Orbigny, pl. 6; but the membrane 
of the umbrella is much more distinct between the upper and lower 
pairs of arms, the dotting of the surface is finer, and the banner is 
much more elongated, with the series of cupules much less definite and 
extensive around it. From A. tuberculata it differs in having a longer 
siphon, much greater number of cupules, and a differently formed 
banner membrane. The joint-like flexure of the first pair of arms is 
different from what is described of any other species. 
Figure 585, the animal, and its details. 
OcTopus MEGALOcYATHUS, (Couthouy MS.) (Gould). 
Corpus ovatum, lave, chocolatum lineis cinerets marmoratum, mem- 
brand laterali angusta quasi natatorid munitum: caput angustum: 
ocult prominuli: siphon bulbosus, curtus: os magnum, rostris nigris: 
umbella amplissima: brachii longissimi ; acetabulis confertis, maxt- 
mis. 
Body ovate, smooth, the tunic forming a narrow, membranous 
