250 ORGANIC REMAINS. 



centre. Its knobs are more strong and prominent than those of the 

 last shell. — No. 3, PI. XIII, is another distinct species ; and it is the 

 most common of our knobbed ammonites. The button and loop 

 marking continues to the centre, as in the last shell ; but the centre, 

 though depressed, is far from being so deep; the body of the spire is 

 more round, the knobs are generally much smaller, and the ribs finer. 

 — If we name No. 9, PI. XIII, a. armatus, we may call this species a. 

 suharmatus ; and No. 11, PI. XIV, a. perarmatus. — ^We have a frag- 

 ment of a large shell, that has measured four inches in diameter, of a 

 species closely allied to a. subarmatus, but thicker, and more deeply 

 umbilicated. It has the termination of the outer whirl, shewing a 

 part of the reflected lip ; but instead of resembling the outer whirl of 

 Sowerby's a. armatus, it is marked with very small and simple knobs, 

 less than those of the next whirl. Perhaps it is only a variety of a. 

 subarmatus. 



Figures 4 and 5, PI. XII, represent fragments of two knobbed 

 ammonites that are rare and singular. No. 4, which is from the lower 

 part of the aluminous strata, is part of the outer whirl of an ammonite 

 that has measured about ten inches in diameter. Its aperture or 

 section is subtriangular, the back being not rounded but with two 

 acute angles, and the sides sloping inwards, especially one side, which 

 is more strongly ribbed and knobbed than the other. The knobs on 

 the plainest side, in this specimen, consist chiefly of galena, a sub- 

 stance which we noticed (p. 124) as occurring in the dogger, and 

 which is not uncommon in the petrifactions of the aluminous strata. — • 

 No. 5 is from the calcareous sandstone below the oolite, on Silphoue 

 moor. It has belonged to an ammonite equally large, and with larger 

 ribs and knobs, placed at greater distances. The back is somewhat 

 rounded, and that and the intervals between the ribs are striated^ 

 whereas in No. 4 they are smooth. Unless more appropriate names 

 can be found, when entire specimens are obtained. No. 4 may be 

 termed a. suhtriangidaris, and No. 5, a. Silphouensis. 



