A. E. Verrill — North American Cephalopods. 425 



Conspectus of the Families, Genera and Species of Cephalopoda, 

 included in this 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. 



Cryptodibranckiaia Blainville, Diet. Sci. Nat., vol. xx.xii, p. 172, 1824. 

 Acetahulife)-es Ferns, k 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(3<T&j, Catal. Brit. Miis.. 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. 

 INIantle 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, pi'ovided, 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: 



Decacera. — Having, inside the circle of eight sessile arms, two long 

 tentacular arms, with suckers or hooks on the distal portion. Suckers 



