A. F. Verrill — North American Cephalopods. 
425 
Conspectus of the Families, Genera and Species of Cephalopoda, 
included in th is paper. 
In the following synopsis the species that have actually been 
proved to belong to the fauna of the northeastern coast of America, 
or the waters adjacent, are numbered serially. They have all been 
personally studied by me, except Taonius pavo. 
Subclass DIBRANCHIATA. 
Cryptodibranchiata Blainville, Diet. Sci. Nat., vol. xxxii, p. 172, 1824. 
Acetabuliferes Ferus. & D’Orb., 1835; Cephal. Acetab., pp. v, xxxv, 1. 
D’Orbigny, Hist. Cuba, Moll., p. 5, 1853. 
Dibranchiata Owen, Trans. Zool. Soc. London, vol. ii, p. 103, 1838. 
Antepedia Gray, Catal. Brit. Mus.. Moll., vol. i, p. 3, 1849. 
Branchial cavity large, containing a single pair of large, highly 
specialized gills, each having a muscular branchial heart at its base. 
Mantle very muscular. Siphon completely tubular, with or without 
an internal valve, and used in locomotion. The interior lateral or 
basal lobes of the siphon are flexible, and capable of acting as valves 
to close the opening of the branchial sac by pressing against the in- 
side of the mantle when it contracts. The jet of water, thus forced 
through the siphon, by its reaction propels the animal backward or 
forward, or in any direction opposite to that in which its flexible 
extremity may be turned. 
The body varies in form from subspherical to long-conical ; sides 
often with fins. Mantle destitute of an external shell. The internal 
shell, when present, is dorsal, and may be either horny or calcareous. 
Sessile arms in four pairs, around the head, provided, on the inner 
surface, with suckers or with hooks (modified suckers). Eyes highly 
developed. Mouth with a sharp, horny beak, the upper jaw shutting 
into the lower one; mandibles hollow, supported by strong internal 
cartilages. Odontophore with seven (or rarely five) rows of sharp 
teeth. An ink-sac, which opens near the end of the intestine, at the 
base of the siphon. 
This subclass includes two very natural divisions: 
Jdecacera. — Having, inside the circle of eight sessile arms, two long 
tentacular arms, with suckers or hooks on the distal portion. Suckers 
