388 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 PHILONEXID^ D'Orbigny. 



Philonexidce (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 entise 

 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, Thier-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 ©f the 

 male is developed in a pedunculated sac. 



