14 ZOOLOGY OP THE VOYAGE OF H.M.8. SAMAKANG. 



{ac ac) differ from the short, terminal, subcircular, true fins in Cranchia and Loligopsis, 

 in having their plane transverse to the axis of the body instead of parallel with it : their 

 base is attached, in the dorso-ventral direction of the trunk, to the sides of the terminal 

 disc, as shown in fig. 9. Their structure is fibrous, the fibres are collected into fasciculi, 

 directed from the base to the free margin of the appendage ; they are probably contractile, 

 but the ultimate fibres are smooth, more minute than those of voluntary muscle, and devoid 

 of transverse striae. The disc adheres pretty closely to the epithelium of the part of the shell 

 which it conceals. The appendages are part of the disc, which has very little organic con- 

 nection with the terminal lobes of the mantle. In the specimen obtained by Mr. G. Bennett 

 (fig. 3 and 9), the surface of the integument differs in a well-marked degree from that in 

 Capt. Sir E. Belcher's or Mr. Cuming's specimens. Instead of being smooth, it is pitted by 

 small close-set angular depressions, which give a well-marked reticulate character to the 

 whole surface of the true mantle. The surface of the cellular disc and its appendages is 

 quite smooth. I regard the character of the skin in the mantle of the Spirula just described, 

 as indicative of distinction of species, and propose for it the name of Spirula reticulata. 

 The general shape of the mantle differs from that of the Spirula australis, obtained by 

 Mr. Percy Earl in New Zealand, in so far as that, instead of being compressed laterally, it 

 is broadest from side to side ; the difference is well shown in the two figures 8 and 9 ; but 

 I do not lay stress upon it in the question of their specific distinction, on account of the 

 mutilated state of the specimen of Spirula reticulata. 



Whether the difference in the development of the appendages of the terminal disc in the 

 Spirula australis (fig. 2 and 8) and Spirula reticulata (fig. 3 and 9) be specific, or due to 

 accident, may be questioned ; but from the dotted character of the integument in the figures 

 of M. de Blainville's specimen (fig. 15*), in which those appendages are as well developed as 

 in Spirula reticulata, it might be suspected that the integument presented a similarly 

 reticulate surface ; and this may, perhaps, account for the differences in the condition of the 

 anus and the fins, observable in fig. 15*, copied from M. de Blainville's Memoir, and in fig. 11, 

 which gives a similar view of the parts in Sir E. Belcher's specimen. 



Whether the terminal disc be a normal generic character of Spirula, cannot be con- 

 clusively determined from the actual evidence : it has the character of an adventitious 

 growth, and is certainly not a part of any of the organs of the vegetal or animal functions : 

 the influence of the appendages of the disc in the locomotion of the Spirula reticulata must be 

 feeble, if any ; in the Spirula australis (fig. 2 and 8) they could have had none. Is the disc with 

 its appendages a sexual character ? It might serve for the attachment of the cluster of ova 

 after their extrusion, and be peculiar to one sex : that of M. de Blainville's specimen was 

 female. I regret that all my pains failed me in determining the sex of Sir E. Belcher's 

 specimen ; had it been unequivocally a male, it would have supported the hypothesis of the 

 sexual character of the appendages in question, since it does not possess them, and seems not 

 to have possessed them. 



