58 Zoological Society : — 



as differing essentially from the shell commonly known as Nautilus 

 utnbilicatus. A more careful examination satisfied me that they 

 were quite distinct ; and I made out a comparative description of 

 them, intending to designate the newly observed one by the name 

 texturatus, on account of its finely reticulated surface. But on re- 

 ferring to the several figures of N. umbilicatus, I found that the 

 figure of Lister, which represents the shell originally named umbili- 

 catus, presented all the characteristics of the reticulated shell, while 

 all other figures represented the smooth, shining shell ordinarily 

 bearing that name. From both the figures and descriptions of 

 authors, I am led to believe that the shell originally observed by 

 Lister has not been recognized by conchologists since his day. Every 

 writer except Favanne expressly speaks of his shell as smooth (Isevis, 

 glatte), and his figure clearly refers to the common shell. On the 

 supposition, then, that these are two distinct species, it is proper to 

 restrict the term applied by Lister to the shell represented by him, 

 and to substitute another for the shell ordinarily named umbilicatus. 

 The term scrobiculatus indicated in manuscript by Solander, and 

 adopted by Dillwyn, and which has been placed by others as a syn- 

 onym, may be appropriately restored to this species. 



The principal differences between the two shells are as follow. 

 Taking the common shell, so well represented in Sowerby's ' The- 

 saurus,' as a standard, the other shell, which we take to be the 

 genuine umbilicatus of Lister, is more ventricose, the sides being 

 nearly parallel, and the periphery broadly rounded ; the aperture is 

 nearly quadrate rather than oval, the posterior angles being nearly 

 right angles ; the umbilicus is rather larger, its walls nearly perpen- 

 dicular, in no degree cup-shaped ; its marginal angle very slightly 

 rounded, the edges of each whorl broadly spreading over the prece- 

 ding whorl, and it is in all cases clearly pervious ; the surface, instead 

 of appearing smooth and shining, with only some distinct traces of 

 revolving strise near the aperture, has a dead, unpolished aspect, and 

 is everywhere conspicuously reticulated with numerous, crowded, 

 well-impressed, revolving lines ; the colouring, instead of a lively 

 ochreous, has a dusky smoky hue, and the chestnut-coloured flam- 

 mules are numerous and delicate, numbering as many as five to the 

 inch in place of three in the scrobiculatus. Li all the specimens of 

 the latter which have come under my observation, the sides are con- 

 spicuously undulated by a series of distinct waves, in the direction 

 of the lines of growth, which are wholly wanting in umbilicatus. 

 The most obvious distinctive marks then are, in the former, the shi- 

 ning surface and waved sides ; and in the latter, the numerous small 

 flannnules, dead surface, and well-marked revolving strise. These 

 revolving strise are plainly indicated on the figure of Lister ; and 

 that they are not merely a style of the engraver's art, but are in- 

 tended to indicate something in nature, may be inferred by comparing 

 the figure with that of X. Pompilius, in immediate proximity, the 

 surface of which is really like that of scrobiculatus. The best of the 

 three specimens examined by me, is now in the possession of Hugh 

 Cuming, Esq., and an inspection of it will fully confirm the above views. 



