PEOF. OWEN ON NEW AND EAEE CEPHALOPODA. 145 



The free (anterior) border of the mantle, or body-wall, is even, not produced as in most 

 Loliffinidw into a point, either at the mid line of the dorsal aspect (PI. XXVIII.), or at 

 any part of the ventral one. The part of the funnel projecting from the latter aspect, 

 rests in a recess on the corresponding surface of the head, like a cannon in its carriage. 

 Such provision, added to the complex basi-lateral joints of the expulsatory tube, must, 

 by increasing its resistance to the force of the ejected respiratory current, correspondingly 

 increase the reacting force of that ejection in the movement of the mollusk. 



The fins (ib. e, e) are attached to two fifths of the terminal part of the body ; their 

 united breadth is twice that of the length attached. They are relatively larger, 

 more powerful, organs of natation than in either of the above-cited species of 

 Ominastrephes. 



The outer circxilar lip has its attachment to the bases of the arms strengthened, as in 

 LoJicjopsis, by narrow muscular ridges or frsena, which are here continued at one end 

 upon the inner side of the base of the arm for a short distance, ending in a point, and 

 at the other end extend to the apex of the triangular process (ib.y) of the outer lip. 

 These labial processes are not acetabuliferous, as in many Squids ^ The two inner lips, 

 answering to those in Ocfopodidce, are also present. 



The chitinous substance of the beak is rather thin, but hard enough at the sharp- 

 pointed tip for its prehensile function in this piscivorous Cephalopod. The longer 

 (under or ventral) mandible (ib. v) shows basi-lateral expansions notched at the hind 

 border. The shorter (dorsal) mandible is without such side plates. 



The acetabula are in a double alternate series on each arm, are relatively small, sub- 

 dilated at the base, which is attached by alongish subcentral pedicle (PI. XXVIII. fig. 2) ; 

 the cavity is bounded by a slightly tumid circular lip lodging the base of a hoop of 

 chitine, the free border of which is denticulate, with some of the teeth longer than the 

 rest. 



The acetabuliferous expansion of the tentacles (ib. fig. 1, t) supports a double alternate 

 row of larger, similarly armed, subsessile cups, and a third series of somewhat smaller 

 ones. These diminish in size and number towards each end of the cupped surface. 



In most species of Ommastrephes one or more pairs of the ordinary arms have the 

 outer surface, or that opposite the cup-bearing one, not rounded, but ridged longitu- 

 dinally, the two sides inclining from the acetabuliferous borders to such ridge. In 

 Ommastrejihes sagittatus the ridge is slightly prominent in the second pair, and 

 partially produced in the third pair of arms, forming a narrow dorsal fold or " velum." 

 In 0. iartramii the fold, or fin-like development of skin is continued from the wliole 

 length of the dorsal ridge, and a second fold or " velum " is developed from the outer 

 border of the series of suckers in the second and third pairs of arms. 



' " Descriptions of some new and rare Cephalopoda," Proceedings of tlie Zoological Society, 8vo, 1836, 

 p. 106. " In this repetition of the structure of the external series of cephalic processes there is an evident 

 analogy to the different series of labial processes oi Nautilus.'' — Ibid. 



