28 Mr. T. G. Ponton on Pyrula (Fulgur) carica 
bed inseparable by any great distinction from, and under, sands 
full of the Potton-Sand fossils*. 
A discussion of the whole question and descriptions of the 
fossils are given in my ‘Geology of the Country round Cam- 
bridge.’ It may be here stated that this investigation led to 
proposing the following classification of the secondary strata :— 
Chalk. 
Cretaceous... / Greensand. 
Gault. 
Shanklin (or Lower Green) Sand. 
Psammolithic } Wealden { Potton? and Wicken and 
(or Siliceous) ) Purbeck | Farringdon beds? 
Portland. 
ae Kimmeridge Clay. 
ig tor} Coral Rag and Gamlingay Clay. 
erspatoic)«** | Oxford Clay. 
Great Oolite. 
Inferior Oolite. 
Lias. 
Trias. 
Oolitic ...... 
While these divisions mark approximately the greater physical 
breaks and the periods when great changes were made in phy- 
sical geography, it happens almost as a necessary consequence 
that there is a linking of the life between each of the six great 
groups of formations here indicated. 
V.—Remarks on Pyrula (Fulgur) carica (Lamarck) and Pyrula 
(Fulgur) perversa (Lamarck). By T. Granam Ponton. 
AxutHovueH fully alive to the responsibility which rests upon an 
one who presumes to doubt the specific value of old and well- 
known forms, I nevertheless venture to submit the few following 
remarks to the consideration of other conchologists. 
Having for some time past been engaged in re-arranging the 
collection of shells in the museum of this city, and having paid 
particular attention to the species comprised in the Lamarckian 
genus Pyrula, I have reluctantly come to the conclusion, for 
reasons to be afterwards mentioned, that Pyrula perversa (La- 
* At the meeting of the Cambridge Philosophical Society, May 27, 1867, 
a paper was read “‘ On the association of Potton-Sand fossils with those of 
the Farringdon Grayels in a phosphatic deposit at Upware on the Cam; 
with an account of the superposition of the beds, and the significance of 
the affinities of the fossils.” This series I propose to name the Wicken 
and Herrimere group. I have already obtained 120 species, including 
many continental species not previously recorded in Britain. 
