BY WILLIAM A. HASWELL, 545 



inches; this part was laterally compressed; at its basis its measure 

 from the dorsal to the ventral side was found to be 1 inch, 10 

 lines; from the right to the left side only 1 inch." He adds "This 

 part was proved to me by dissecting it to be formed by the union 

 of four unusually developed tentacular slips, one of which was 

 shorter and more free, the three other chiefly composing the sin- 

 gular body." 



From the dimensions here given and the figures accompanying 

 the paper it would appear that Van der Hoeven had under obser- 

 vation a completely or nearly completely developed specimen. Such 

 mature specimens are comparatively rare; and all the male 

 Nautili that have been made the subjects of other published 

 descriptions appear to have been immature, so that some important 

 and interesting points in the structure of the fully-developed 

 spadix have been overlooked. 



In the larger of the two mature male specimens I have 

 had the opportunity of examining (in which the greatest 

 diameter of the shell is 6J inches) the total length of the 

 organ is 3 -J inches, the greatest breadth about IJ inch, and 

 the thickness a little less than an inch. The four tentacles com- 

 posing it (Plate xlviii. fig. 1) are all very strongly modified in 

 different directions. One of them, as observed by Van der 

 Hoeven, is separate from the rest except at the base. It is shorter 

 than the "others, and does not seem to be capable of being 

 retracted, its sheath being very short: its free part, which is 

 spathulate towards the extremity, lies under shelter of a wide fold 

 extending backwards over it from the sheath of the tentacle 

 which I have numbered 3. Tentacles 2, 3, and 4 have their 

 sheaths united, but the tentacles themselves are quite separate. 

 No. 2 is a thick, solid, muscular cylinder, or rather elongated, 

 blunt cone, probably not capable of being extended to any great 

 distance; the cavity of its sheath is very wide. No. 3 is elon- 

 gated and laterall}^ compressed, marked on its posterior and external 

 surface with numerous transverse ridges. No. 4 presents the 

 most remarkable modification; it is thick and cylindrical towards 

 the base, becoming compressed towards the free end. The outer 



