A. E. Verrill — North American Cephalopods. 
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 the third pair is hectocotylized in the 
male. Sometimes the entire arm is modified and sometimes the tip 
only. 
Family PHILONEXID JE D’Orbigny. 
PhilonexiJce (pars) D’Orb., Mol). Yiv. et Fos.. i. 199, 1845 (t. Gray). 
Gray, Catal. Moll. Brit. Mus., i, p. 24, 1849. 
Keffersteiu, in Bronn, Tliier-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 the siphon laterally by a com- 
plicated prominent cartilage or button fitting in a corresponding 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 Steenstrup. 
Parasira, Kefferatein, in Bronn. 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 fits into a button- 
hole), so that it can be separated only with considerable difficulty. 
