66 Mr. J. Lycett on Fossil Shells from the 



Oolite ; this addition would still further reduce the per-centage 

 of those which pass upward to the latter formation. 



For remarks on particular species the notes which accompany 

 the Tables should be consulted, but some further observations 

 upon the several families of shells may here be given. The 

 Leckhampton shells as a whole are remarkable for their diminu- 

 tive size : this remark is not only applicable to those species which 

 are likewise found in the lower and upper divisions of the same 

 formation, but to those also which are found in the same forma- 

 tions at Minchinhampton. Upon the whole it may be stated that 

 there is a nearer approximation between the Great Oolite and 

 Leckhampton shells than between those of the two formations 

 at Minchinhampton. As compared with the upper and lower as- 

 semblages, the middle is characterized by an entire absence of 

 the Pholadomyas, the Homomyas, the Gresslyas, and I had almost 

 said of Ammonites, Belemnites and Nautili, genera which con- 

 stitute so large a proportion of the other assemblages, in this 

 respect presenting a striking accordance with the contents of the 

 shelly beds of the Great Oolite. Again, the large number of 

 NerinecB and Cerithia, though differing specifically from those of 

 the Great Oolite, tend much to separate it zoologically from the 

 upper and lower assemblages, where they are few and rare. Mr. 

 Brodie's collection has a single Nautilus and Belemnite ; my own 

 has four Ammonites of one species, and a single Nautilus ; their 

 presence under such circumstances is a sufficient indication of 

 the solitary and perhaps accidental nature of their occurrence, a 

 proof in fact that they did not live and propagate in the middle 

 division. The Rostellarice, though few in number and differing 

 specifically from those of the Great Oolite, serve also to mark the 

 separation of the assemblage from other Inferior Oolite groups, 

 and its approximation to the conditions of sea-bottom under 

 which the Great Oolite shelly beds were deposited ; but the most 

 striking circumstance which tends to the same conclusion is the 

 occurrence of a great diversity of forms in the family of the 

 Patelloidea, which appears to be altogether absent in the upper 

 and lower series ; of the fourteen species it will be observed, that 

 no less than six are specifically identical with Great Oolite forms ; 

 and what renders this fact the more worthy of notice is, that the 

 entire family are absent in the Inferior Oolite contemporaneous 

 beds at Minchinhampton. The Terebratulre, which usually are 

 of much importance in the determination of particular groups of 

 rocks, are abundant in this division only in the bed of Oolite 

 marl; but in localities where the marl is consolidated into a 

 Cream-coloured mudstone, or where a considerable number of 

 other genera of shells are present, the Terebratulce are compara- 

 tively scarce ; the genus however is one which conduces much to 



