20 SECOND SUPPLEMENT TO THE CRAG MOLLUSCA. 



PLEUROTOMA SENILIS, 8. Wood. 2nd Sup., Tab. Ill, fig. 2 a, b. 



PLEUROTOMA SENILIS, S. Wood. 1st Supplement, p. 42, tab. v, fig. 5. 

 ABCTICA ?, Adams. p. 45, t. vi, fig. 9. 



VIOLACEA, M. & A. 



Locality. Red Crag, Sutton and Waldringfield. 



The original specimen, figured in my first Supplement, was very much worn, but 

 some better preserved specimens from the Red Crag have been obtained by Mr. Canham. 

 That which I have now figured as 2 b was the most perfect, and has since been lost by 

 him, but having while it was in my hands had a drawing made of it I am enabled to give 

 the figure 2 b from this. The specimen figured in Tab. V of my first Suppl. was so 

 much rubbed that some uncertainty attaches to its identification with the shells now 

 figured, and under these circumstances it is our present shell that I desire to distinguish 

 by the specific name of senilis. The fragment, No. 9, figured by me in Tab. VI of my 

 first Suppl. under the name of arctica, seems to be one of a much worn specimen of the 

 present species. They are all derivative in the Red Crag, but may, I think, not impro- 

 bably have been derived from the Coralline, though nothing identical with them has yet 

 been obtained from that formation. Under the circumstances explained above, I have 

 removed the name of P. violacea from my Synoptical list. 



PLEUROTOMA CATENATA, A. Sell, MS. 2nd Sup., Tab. Ill, fig. 5. 



Axis, j^-ths of an inch. 



Locality. Cor. Crag, Gedgrave. 



The above figure is taken from a specimen in the Cabinet of Dr. Reed, which was 

 obtained from the Cor. Crag by Mr. A. Bell, who had assigned it the above name 

 in MS. 



There is so much uncertainty attending many identifications of the species of this 

 genus that I prefer giving the figure of the shell with Mr. A. Bell's assignment of it to 

 expressing any opinion of my own about it. 



The shell has eight volutions, very slightly convex, indeed nearly flattened ; apex 

 obtuse ; embryonic whorls smooth ; there are two rows of nodules, above which is the 

 sinus and two smaller spirally nodulous lines ; base of volution covered with prominent 

 spiral lines ; aperture ovate, with a canal of moderate length ; the ornamentation, though 

 not very well defined, appears to be its only distinction. The specimen figured is the 

 only one which I have seen, and is by no means perfect. 



