EEPOET ON THE CEPHALOPODA. 67 



Family II. A M p H i T R E T i d ^, n. fam. 

 Amphitretus^ Hoyle. 



This genus possesses the character, unique amongst Cephalopoda, of having the mantle 

 fused with the siphon in the median line, so that there are two openings into the branchial 

 cavity, one on either side, whence the name.^ Since only one species is at present known, 

 it is unnecessary to give a more detailed generic diagnosis. 



Amphitretus pelogicus, Hoyle (PI. IX. figs. 7-9). 



1885. Amphitretus pelagians, Hoyle, Diagnoses I., p. 235. 



1885. „ „ Hoyle, Narr. Chall. Exp., vol. i. p. 271, fig. 106. 



1885. ,, ,, Hoyle, Prelim. Kep. I., p. 113, woodcut. 



Habitat.— '^ta.tioii 170, ofi" the Kermadec Islands, July 14, 1874; lat. 29° 55' S., 

 long. 178° 14' W. ; 520 fathoms; volcanic mud. One specimen, sex(?). 



The Body is short, rounded, of gelatinous consistency, and semitransparent. The 

 mantle adheres to the sides of the siphon, so that the mantle-opening, which is single in 

 all other known Cephalopods, is here divided into two pocket-like openings, which lie one 

 beneath each eye, and extend less than halfway to the siphon, which is very long and 

 narrow, and extends forwards anteriorly to the margin of the mantle, for a distance 

 almost equal to the length of the body, and is a little swollen at the extremity. 



The Head is indistinguishable from the body, except by the possession of the eyes, 

 which are situated near together on the dorsal surface ; they consist of a larger basal 

 spheroid, through the walls of which pigment is clearly visible, upon which stands a 

 smaller very prominent spheroid, white, opaque, and of glistening surface. 



The Arms are equal, and rather more than twice as long as the body ; they are 

 slender, and taper at first gradually and then more rapidly to comparatively blunt points. 

 The umhrella extends more than two-thirds up the arms, and is thin, delicate, and trans- 

 parent (much damaged in the present instance). The suckers are firm, muscular cups 

 embedded in the softer tissue of the arms, as in Cirroteuthis ; there are about twelve 

 placed at some distance apart on that portion of the arm up which the web extends, and 

 eleven closely set, and showing a tendency to biserial. arrangement on the free extremities. 

 There are no cir7'i, nor is there any trace of the formation of a hectocotylus. 



1 iifi0irQT,r<i;, with, double entrance. 



- Functionally, if not structurally, this arrangement may he compared with tlie median septum which is 

 found in the hranchial cavity of Octopus, Eledone and other genera, and is seen carried almost to the margin of the 

 mantle in Alloposus mollis, Verrill (Ceph. N. E. Amer., pi. 1. figs. 1, 2). 



