MARINE MOLLUSCA OF THE UNITED STATES. 10) 
Body elongate; back with a central, transparent line over the 
keel of the shell. Fins rhombic. Sessile arms slender; dorsal 
pair rounded externally, with a slight fin on the upper part; the 
second, third, and fourth pairs finned on the outer side nearly the 
whole length. Tentacular arms with siz large hooks. Shell dark- 
brown, lanceolate, pennate, with a short central keel above and 
ridge beneath, thin. 
Gulf Stream, Indian Ocean, New Zealand. 
Genus ONYCHIA, Lesueur. 
Journ. Philad. Acad., i. 98, 1821; ii. 296, 1822. 
In this genus the body is red and spotted; the tentacular arms 
scarcely enlarged at the ends. Like most other genera of this 
family, and other pelagic forms, it is crepuscular, darting along 
the surface of the ocean toward nightfall, and preying upon small 
fishes, floating crustacea and acalephz that swim near the surface. 
1. O. cARDIOPTERA, Péron. Fig. 6. 
(Loligo.) Voy. Atlas, t. 60, f. 5. 1804. 
Sepiola cardioptera, Lesueur, Journ. Philad. Acad., ii. 100. 1821. 
Onychia caribea, Lesueur, ibid., ii. 98, t. 9, f. 1, 2. 1821. 
Onychoteuthis Leachii, Férussac, Céph. Acét. Onych., t. 5, f. 4, 7. 
Body large, oblong, narrowed and prolonged behind. Sessile 
arms unequal, relative lengths 3, 2, 4,1; cups in two alternating 
lines. Shell rather broad, sides rounded. 
Southern Atlantic Ocean; Gulf of Mexico. 
Genus OMMASTREPHES, Orbigny. 
Moll. Viv. et Fos., i. 412. 1845. 
In this genus the sessile arms are conical, subulate, upper and 
lower quadrangular, the others triangular, compressed, unequal ; 
relative lengths 3, 2, 1,4; the cups are very oblique, fleshy, dis- 
tinct; the rings oblique and toothed. 'Tentacular arms not re- 
tractile, short, strong, thick, with a slight longitudinal ridge, 
scarcely enlarged at the end, webbed at the tip. 
Living in the high seas in large troops, nocturnal; the food of 
cetacea and pelagic birds. The sailors call them “ sea-arrows” or 
“ flying-squids,” from their habit of leaping out of the water, often 
to such a height as to fall on the decks of vessels. 
