in the Cephalopoda, 83 



which I state them, I have allowed myself to be guided in part 

 by the succession in which they have occurred to me. 



This, therefore, is the original reason for my commencing 

 with the genus Loligo, Lamk., as I first became aware of this 

 peculiarity by my comparative investigations of our northern 

 species; the continuation of my investigations has, however, 

 shown me that I may naturally start from this genus. 



In the restricted genus LoligOy Lamk. (and therefore wdthout 

 the species upon which D'Orbigny subsequently founded the 

 genus Ommatostrephes) , all the species which I have had the 

 opportunity of examining* have the extreme portion of the fourth 

 left arm (ventral arm) so metamorphosed, that the acetabula or 

 suckers, which in the opposite arm are continued quite to the 

 apex, constantly diminishing in size, here gradually disappear; 

 whilst the peduncles on which they are seated, on the contrary, 

 increase in size, and become converted into long papillae, giving 

 the extreme part of the arm a peculiar, pectinate appearance. 

 These papillae always appear to be most strongly developed on 

 the external margin of the arm, whilst those belonging to the 

 series of acetabula on the inner f margin of the arm retain a 

 trace of sucking-disks for a longer distance. 



In the largest species of the genus LoligOy the so-called 

 Atlantic form of Loligo vulgaris, Lamk., but which is really a 

 distinct species, for which I have, in another memoir, proposed 

 the name of L. Forbesii, Stp., the fourth left arm of the male has 

 twenty-three pairs of acetabula regularly developed and corre- 

 sponding with the suckers on the same space of the right arm ; 

 from the twenty-third pair onwards the size of the sucking- 

 disks suddenly diminishes; and even the twenty-seventh and 

 twenty-eighth pairs have them so small that they can only be 

 distinctly recognized with the aid of a lens; after this the 

 sucking-disks disappear entirely, whilst the muscular root of 

 the peduncle becomes elevated to three or four times its ordinary 

 height, and converted into a conical, elongated papilla. There 

 are about forty pairs of papillae, and therefore the same number 



* Besides the Cuttle-fishes in the two museums of which I have the 

 superintendence, or in which I am interested, namely the Zoological Mur 

 seura of the University [of Copenhagen], and the Royal Museum of Natural 

 History, I have also been enabled, by the kindness of my colleague. Pro- 

 fessor Eschvicht, to make unlimited use of the materials possessed by the 

 Zootomical Museum of the University. 



t Under the terms "inner" and "outer" margins of the dorsal and 

 ventral arms, those will always be understood here which lie nearest to or 

 furthest from the median plane of the animal : in the two lateral pairs of 

 arms I employ the terms " upper" and " lower" to indicate the two corre- 

 sponding margins of the arms, or the series of acetabula standing upon 

 them. 



6* 



