406 Mr. J. Lycett on Fossil Shells from the 



impress an individual or distinctive character upon the assem- 

 blage, or to isolate it from other shelly deposits ; it will be ob- 

 served that of the twelve species two only of them appear to 

 have been continued to the period of the Great Oolite ; the 

 other species do not even seem to be found in the other divi- 

 sions of the same formation, each of which has its distinctive 

 Terebratul(s. 



The vertical range of the several species throughout the middle 

 division is considerable, for with the inception of certain small 

 and very rare species, the same Terebratula may be found to oc- 

 cur at intervals through a vertical thickness of 140 feet of rock. 

 The genera which may be pointed out as most eminently to cha- 

 racterize this division are the CerithiOj the Nerinece, the Trochi, 

 the Solaria, the Cijlindrites, the Melanice, the Rostellariae, the 

 Trochotomce, the Tancredice, and the Terehratulm ; of these tribes 

 all but two belong to the Gasteropoda ; they constitute the great 

 bulk of the univalves, and contain in all fifty-two species, not one 

 of which is found in the Great Oolite. Other genera might be 

 mentioned whose species equally belong to this series, but such 

 have been selected as acquire importance either by the number 

 of their species or by that of the individuals of such species. It 

 may perhaps place the subject in a more striking point of view 

 when it is stated, that of the 108 Gasteropods only 20 are con- 

 tinued to the Great Oolite. The smaller per-centage obtained 

 from the total number of species when compared with a single 

 locality is caused by a large proportion of the shells which are 

 common to the two localities being likewise those which pass 

 upwards into the Great Oolite, thus illustrating the fact, that 

 species which occur in considerable number and have a wide 

 range horizontally, are those which we should expect to find 

 .through a considerable range of beds vertically. 



I would define the limits of the middle or freestone division of 

 the Inferior Oolite as including all that portion of the formation 

 situated between the upper ragstone beds (1, 2, 3 and 4 of Mr. 

 Strickland^s section), and the Ammonitiferous beds or upper por- 

 tion of the lower division. 



Lastly, the general conclusion may be stated to which this 

 comparison has led, that these testacea constitute a zoological 

 assemblage distinguished from those of the other portions of the 

 Inferior Oolite by features as well-marked as those which di- 

 stinguish the fossils of the other great groups (proximate in 

 sequence), which are termed formations, from each other, and 

 that these features, varying in detail, will probably be found to 

 occur, like some other shelly deposits of the oolitic formations, at 

 intervals and over small areas wherever the freestones of the 

 Inferior Oolite are extensively developed. 



