32 SECOND SUPPLEMENT TO THE CRAG MOLLUSCA. 



The specimen figured seems to be intermediate between Natica sordida and Natica 

 Alderi, approaching rather nearer to the latter than the former, but to neither does it 

 strictly accord, having the form and nearly the size of sordida, but without its depression 

 upon the upper portion of the volution. It is also rather more elongated than either, 

 while the left lip is more extended than in Alderi, but rather less so than N. sordida. 

 The shell is strong and nearly ovate, the contour showing but very little depression 

 between the volutions, which slopes from the small and pointed apex. The exterior is 

 smooth with simple lines of growth. As the specimens maintaining these characters are 

 not rare I have ventured to refer them as above, though they bear a resemblance 

 to Natica hemiclausa, a shell very abundant in the older part of the Red Crag at Walton 

 Naze, but this latter has the umbilicus covered by the left lip in specimens that are full 

 grown. 



Natica are extremely abundant in the Butley bed, in association with the various 

 peculiar and northern species of mollusca, which distinguish that newer portion of the 

 Red Crag from the older or Walton portion, and their generally decorticated condition, in 

 which the specimens which I refer to triseriata participate, increases the difficulties 

 which attach to their specific separation. 



I have not the recent species for comparison, and in making my reference to it my 

 dependence is upon the figure and description given by Gould. The coloured markings 

 which induced that author to give to it its name have disappeared in the Crag fossil, if 

 they ever were present. There is also a resemblance between our fossil, and Natica 

 immaculata, Totten, but this Mr. Jefireys refers to N. Alderi, to which species I think the 

 present fossil does not belong. 



In ' Crag Moll.,' vol. i, p. 144, I said, when speaking of Natica varians, " It appears 

 to be quite distinct from Natica hemiclausa, and it agrees in most of its characters with 

 N. varians from Touraine." I am still of the same opinion. In Mr. Prestwich's List, 

 p. 144, N. varians of the Cor. Crag is referred as a variety to N. cirriformis, but 

 N cirriformis is there referred to N. sordida. In Mr. A. Bell's List of the Lower 

 English Crag, N. varians of the Crag is considered as N. helicina, Broc. The same shell 

 is by M. Nyst figured as Natica hemiclausa, Sow. These conflicting opinions afford a 

 proof of the perplexity in which those who study fossil mollusca become involved when 

 occupied with this genus. 



I have in Tab. Ill, fig. 7 a — b, given the representation of another specimen of this 

 genus from the Coralline Crag near Orford, which is in Mr. Cavell's collection. This seems 

 to differ materially from the shell which I have figured as N. helicina from the Red Crag 

 of Walton Naze (' Sup. Crag Moll.,' p. 74, fig. 8 a, b), as it possesses a large and deep 

 umbilicus, and although the front of the shell shows a depression at the suture, there is 

 remaining a small portion of shelly matter, which if continuous would cover this deep 

 suture entirely, and indicate that it possessed this covering feature, which is wanting 

 in N helicina. 



