A. E. Yerrill — North American Cephalopoda. 361 



thick, obtuse posteriorly, usually destitute of fins. Fins, when pres- 

 ent, small, lateral, supported by an internal transverse cartilage. 

 Mantle usually extensively united to the head by a dorsal commis- 

 sure. Siphon without an internal valve. Branchial cavity divided 

 into two parts by a median septum, extending forward to the base 

 of the siphon, but interrupted posteriorly. No olfactory crests. Eyes 

 united to the internal lining of the sockets, so as to be immovable, 

 usually furnished with lids. No outer buccal membrane. Aquiferous 

 pores and cavities usually absent ; cephalic pores sometimes present. 

 Internal longitudinal shell or pen absent. An external shell is pres- 

 ent only in the genus Argonauta. In this case it is formed as a 

 secretion from the inner surface of the expanded distal portion of the 

 two dorsal arms, of the female only, and serves mainly as a receptacle 

 for the eggs. The right arm of tlie third pair is hectocotylized in the 

 male. Sometimes the entire arm is modified and sometimes the tip 

 only. 



Family PHILONEXID^E D'Orbigny. 



Philontxidm (pars) D'Orb., Moll. Viv. et Fos., i, 199. 1845 (t. Gray). 

 Gray, Catal. Moll. Brit. Mus., i, p. 24, 1849. 

 KefEersteiu, ia Bronn, Thier-Reich., iii, 2 B., p. 1449, 1866. 



Body stout, oval, destitute of lateral fins. Branchial opening large. 

 Edge of mantle united to the base of tlie siphon laterally by a com- 

 plicated prominent cartilage or button fitting in a coi*responding pit 

 on the inner surface of the mantle. Dorsal commissure narrow. 

 Head with aquiferous pores communicating with large aquiferous 

 cavities. Arms simple, more or less united by webs. Suckers promi- 

 nent. 



In the male, the hectocotylized arm is developed in a sac, the entire 

 arm being modified, and usually, when perfected, it becomes detached 

 from the body. Probably this arm is lost and regenerated each year. 



Parasira steenstmp. 



Parasira Kefferstein, in Broan. Thier-Reich., iii, p. 1449, 1866. 

 Tryon, Man. Conch., i, p. 104. 



Body short, thick, pouch-like, usually ornamented with raised 

 ridges. Mantle united directly to the head dorsally; laterally con- 

 nected to the base of the siphon by a pit and raised cartilaginous 

 tubercle on each side, which fit corresponding pits and tubercles, 

 near the base of the siphon (something as a button tits into a button- 

 hole), so that it can be separated only with considerable difficulty. 



