REPORT OF COMMISSIONER OF FISH AND FISHERIES. [ 178 ] 
posteriorly, usually destitute of fins. Fins, when present, small, lateral, 
supported by an internal transverse cartilage. Mantle extensively united 
to the head by a dorsal commissure. Siphon without an internal valve, 
united directly to the head. 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 present only in the genus 
Argonauta. In this case it is formed as a secretion from the inner sur¬ 
face of the expanded distal portion of the two dorsal arms of the female 
only, and serves mainly as a receptacle for the eggs. One of the arms 
of the third pair, commonly the right, is hectocotylized in the male. 
Sometimes the entire arm is modified and sometimes the tip only. 
Family PHILONEXID2E D’Orbigny. 
Philonexidoe (pars) D’Orbig., Moll. Viv. et Fos., i, 199,1845 (t. Gray). 
Gray, Catal. Moll. Brit. Mus., i, p. 24, 1849. 
Body stout, oval, destitute of lateral fins. Branchial opening large. 
Edge of mantle united to the base of the siphon laterally by a compli¬ 
cated, 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 prominent. 
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 Steenstrup, Vidensk. Meddel. naturh. Forening, Kjobenhavn, I860, 
p. 333. 
Kefferstein, in Bronn, Tliier-Reich, iii, p. 1449,1866. 
Tryon, Man. Conch., i, p. 104. Verrill, Trans. Conn. Acad., v, p. 361. 
Body short, thick, pouch-like, usually ornamented with raised ridges. 
Mantle united directly to the head dorsally; connected laterally to the 
base of the siphon by a deep pit and a raised, cartilaginous tubercle on 
each side, which fits a corresponding cartilaginous tubercle and pit, near 
the base of the siphon (something as a button fits into a button-hole), 
so that it can be separated only by using considerable force. Arms long, 
slender; web rudimentary. Suckers prominent, in two alternating rows. 
Gill-opening wide. Siphon large, intimately united to the head except 
at its free extremity, which is situated far forward, between the ventral 
arms. A large aquiferous pore, each side of the siphon, at the bases of 
the ventral arms. 
Sexes are widely different. The hectocotylized, third right arm of the 
male is developed in a pedunculated sac. 
