1066 CEPHALOPODA. [Dibranchia. 



ones near each eye ; arms elongated, order of length 2. 1. 3. 4. two 

 dorsal pairs flattened and webbed to their tips. 



Total length, 33 mm. ; length of body, 6-5 mm. ; length of second 

 pair of arms, 23 mm. ; first pair, 15 mm. ; third pair. 13 mm. ; fourth 

 pair, 13 mm. 



Type in the Museo Zoologico, Naples ? 



Hob. A specimen was caught near the Great Barrier Island, and 

 identified by Dr. Hoyle. Mediterranean. 



Genus 2. ARGONAUTA, Linne, 1758. 



Argonauta, L., Syst. Nat., ed. 10. 1758, 708. Type : A. Argo, L. Ocythoe, 

 Leach, 1817: not of Rafmesque. 1814. 



The hectocotylized arm autotomous. The extremities of the dorsal 

 arms are enlarged in the female, and secrete a shell in which the body 

 is contained. The males are very small and naked. Arms subulate. 

 Mantle supported by 2 buttons, fitting into grooves at the base of 

 the siphuncle. The shell is involute, one-celled, brittle, horny, slightly 

 flexible when wet, with a large hemispherical nucleus. 



The argonaut swims with great velocity in a reversed position 

 with the siphuncle directed towards the fore part and keel of the shell, 

 and the velated arms firmly embracing the sides of the shell ; it also 

 crawls along the bottom by the contortions of its simple arms, holding 

 the shell back upwards with the membranous arms, which are bent 

 backwards ; there is no muscular or organic connection between 

 the animal and shell, which, when vacated by the argonaut, floats 

 at the mercy of the waves. 



Distribution. About ten species are known, living in warm seas, 

 and some having a wide distribution. 



Fossil in the Pliocene of Italy. 



KEY TO SPECIES. 



a. Ribs of shell numerous, close ; keel narrow . . . . . . Argo. 



b. Ribs of shell few and distant ; keel broad . . . . . . Mans. 



c. Ribs numerous, tuberculated ; keel rather narrow . . . . tuberculata. 



1. Argonauta Argo (L.), Bolten, 1798. Plate 72. 



Ai-i/oiututii An/o, Linne, Syst. Nat., ed. x, 1758, 708 (in peart) : Bolten, Mus. 

 Bolten., 1798, 70: Lamarck, A.s.V., vii, 1822, 052: d'Orbigny, Ceph. 

 acet., 158, Argonaute, pi. 2, f. 1,2: Reeve, Conch. Icon., xii, 1861, 

 pi. 3, f. 2: Tryon, Man. Conch. (1), i. 138, pi. 47, f. Ill, 112; pi. 48, 

 f. 116, 117: Chall. Rep., xvi, 4, 69: Brazier, Cat. A.M., No. 15, 1 : 

 Pritchard and Uatliff, P.R.S. Vic. (n.s.), x, 243 : Ball, Bull. Mus. Comp. 

 Zool., Harvard, xliii, No. 6, 226, 227. A. sulcata, Lamarck, Syst. A.s.V., 

 1801, 99. A. papyracea, Link, Beschr. Rostock Samml., 1807, 85. 

 A. hattstrum, Dillwyn, Descr. Cat. Recent Shells, i, 1817, 335 (young 

 shell). A. naviformis, Conrad, Journ. Acad. Nat. Sci. Philacl., 1854. 

 2nd ser., ii, 334. A. Bullcri, T. W. Kirk, T.N.Z.I., xviii, 1885 (188<i). 

 138, pi. 4 ; Ball, I.e., 226, 228. 



Animal. Body oblong, smooth ; eyes large, prominent ; arms 

 unequal, order of length 1, 4, 2, 3 ; the dorsal pair elongate, second 



