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SUPPLEMENT TO THE BRITISH 



T. semighbosa and T. carnea, with and without triplication near the front, has been found' 

 by Mr. Tate in the Hibernian Greensand near Belfast, Ireland. 



I have felt and still feel very uncertain with reference to this shell ; for, while some 

 examples resemble flattened specimens 01 T. semighbosa, others cannot be distinguished 

 from T. carnea, and every variation connecting the two extremes can be obtained. 



T. carnea is a very characteristic fossil of the White Chalk with Belemnitella 

 mucronata, while T. semighbosa occurs in the Lower Chalk and Red Chalk of Speeton, in 

 Yorkshire, and in the upper part of the Red Chalk of Hunstanton. Now, according to 

 Mr. Tate 1 — 



" 1 . The Cretaceous rocks of Ireland are referable to two formations, the Hibernian 

 Greensand and the Upper Chalk. 



" 2. The Hibernian Greensand is divisible into well marked lithological and palaeon- 

 tological zones, and is the equivalent in miniature of the ' Etage Cenomanien ' of 

 D'Orbigny. 



"3. The zone of Exogyra conica represents the basement-beds of the ' Etage 

 Cenomanien ' of the French geologists, and is approximately equivalent to the Greensand 

 of Blackdown. 



" 4. The zone of Ostrea carinata represents most certainly a portion of the Upper 

 Greensand of England and the Lower Cenomanian of Normandy. 



" 5. The Chloritic Sands and Sandstones have, on the whole, a fauna possessing an 

 Upper- Greensand facies, many species, however, pointing to higher zones. 



" It is very probable that the Chloritic Sands of Woodburn (the ' Zone of Inoceramus 

 Crispi ?') may be inferior to the Chloritic Sandstones of Colin Glen, the ' Zone of Exogyra 

 columba.' These two zones, however, never come in contact. 



" 6. The Upper Chalk contains three subdivisions : 

 " a. Zone of Ananchytes gibbus. 

 " b. Spongarian Zone. 



" c. White Limestone, or ' Zone of Ammonites Gollevillensis! The White Lime- 

 stone certainly represents the Upper Chalk of Norwich and the ' Craie de Meudon 

 and some of its fossils point even to a higher parallel — that of the Maestricht 

 Chalk." 



Now, we find in Ireland T. carnea in its true stratigraphical position, namely, in the 

 hardened White Chalk of Antrim. Lower down, in the Hibernian Greensand near 

 Belfast, we find true T. semighbosa and the intermediate form, or what we will provisionally 

 designate as the var. Hibernica. 



1 See R. Tate, " On the Correlation of the Cretaceous Formations of the North-East of Ireland," 

 * Quarterly Journal of the Geol. Soc.,' vol. xxi, pp. 33, 36, 1864. 



