in the Cephalopoda, 91 



of the opposite side, or between the arms of the male and 

 female. 



In Sepia inennis, Van Hasselt, from the Indian Ocean, of 

 which the Museum only possesses one male specimen, and this 

 a small one, of hardly 4 inches in length, I find this peculiarity 

 still more remarkably developed. The lower half of the arm 

 (see PI. II. fig. 8) possesses no suckers at all, but its whole 

 breadth is metamorphosed in the same way as the outer side of 

 the corresponding portion of the arm in Sepia officinalis, a num- 

 ber of pits being arranged distinctly enough in rows by more 

 prominent folds of skin, which pass transversely across the arm. 

 The strongest transverse folds appear to indicate the position of 

 the muscular parts, to which the peduncles of the acetabula are 

 attached; and from their number, we may suppose that about 

 twenty transverse rows of suckers have disappeared. Both mar- 

 gins of the arm have a tendency to fold together, and thus, as 

 it were, to form a very long sucking or grasping plate. The 

 specimen referred to, from which fig. 8 is drawn, was unfor- 

 tunately somewhat fl.abby, and not very well preserved ; a better- 

 preserved specimen may perhaps exhibit a trace of the suckers, 

 the existence of which I have thought myself compelled to deny. 

 At any rate, this structure, in an Indian species of Sepia, renders 

 it probable that the peculiarities above described in Sepia officii 

 nalis do not occur in this species alone, but that we have in 

 this case to do with a phsenomenon occurring in the whole^genus 

 Sepia. 



Of three other species of this genus I only possess female 

 specimens; and in these, as in the females of the two preceding 

 species, the four series of suckers pass up to the base of the arm, 

 constantly increasing in size. 



With the genus Sepia, D^Orbigny groups the two principal 

 genera of the small shore Cuttle-fish, — Sepiola, Leach, and 

 Rossia, Owen; but, as regards the peculiarities of the arms, 

 which we are investigating here, they are widely separated from 

 each other, as the following will show at once. 



In a male Sepiola Rondeletii, D^Orb., I found the following 

 peculiarities. Of the first, or dorsal pair of arms, that of the 

 right side bore very small suckers in two rows up to the apex ; 

 and these, which became smaller quite regularly upwards, did 

 not attain one-fourth of the size of the large globular acetabula 

 which are found on the second and fourth pairs of arms, espe- 

 cially on their middle portion ; in this they agreed with the 

 suckers of the third pair. In this unequal development of the 

 acetabula this male Sepiola of mine also agrees with fig. 5 of the 

 first plate of Sepiola in the great work of Ferussac and D'Or- 

 bigny. The arm on the left side, however, differed not only 



