98 



from the " Productive Coal Measui'es," or Division A., of the Sucia 

 Islands,* in the summer of 1874. The most perfect of these has 

 already been briefly characterised on page IT of this volume, but 

 the statement there made that " the siphuncle is situated a little on 

 the outside of the centre of the septa," has since been found to be 

 incorrect, and the inferences drawn under this impression, viz., that 

 the shell is probably only a variety of Nautilus Atlas (nobis), and that 

 it agrees almost exactly with Meek's diagnosis of the Nebrasca shell 

 figured as N. elegans, are, of course, no longer tenable. When the first 

 description of the Sucia Island Nautilus was written, the lower part of 

 the only septum in which the siphuncle could be traced was covered by 

 the matrix, and sufiicient allowance was not made for the depth of the 

 emargi nation at its base. "While endeavouring, subsequently, to remove 

 part of the matrix, a piece of the septate portion became detached in such 

 a way as to expose the whole of the convex surface of this septum, the 

 eighth from the aperture, most of which had previously been hidden from 

 view. On account of the rounding oflf of the margin it is difficult to 

 give very accurate measurements, but, as nearly as can be ascertained, 

 the height of this septum, in the centre, is nine lines, and the middle of 

 the siphuncle is about five lines from the outer and four from the inner 

 margin of the septum. In the other specimen, which is a cast of the 

 body chamber, with one of the so-called air chambers attached, the whole 

 of the convex side of the last septum but one is fully exposed. Follow- 

 ing its convexity throughout, along the median line, the total height of 

 this septum is twenty-three lines, and the centre of the siphuncle is 

 thirteen lines distant from the periphery and ten lines from the inner 

 margin of the septum. Thus it would appear that the siphuncle is 

 placed a little on the inner side of the centre, at a distance from it 

 about equal to its own diameter. 



This species seems to be more closely allied to the Nautilus Albensis 

 and N. Neckerianus, as described by Pictet and Campiche in the Paleon- 

 tologie Suisse, than to any of the ribbed Nautili from the Cretaceous 

 rocks of North America. In N. Albensis the siphuncle is situated at 

 one-third the height of the septum, on the inner side of its centre, and 

 this is the only difference at present obvious between it and N. 8uciensis. 

 The position of the siphuncle apjDcars to be precisely similar in N. 

 Neckerianus and N. Suciensis, but the former shell has much more 



* The words "Sucla Islands,*' as appll d to specimens coUec'ed by Mr. Richardson, are 

 Invariably employed as an abbreviation lor south-west side of the largest island or the Sucla 

 group. 



