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BRITISH FOSSIL TRIGONLE. 



Collyweston and Wakerley, in Lincolnshire Limestone ; these have the costse unusually 

 minute, numerous, and faintly denned ; they appear to be examples of dwarfed adult 

 forms. Other localities noted by Mr. Sharp in his memoir on the Oolites of Northamp- 

 tonshire ('Quart. Jour. Geol. Soc.,' May, 1873), are Ravens Wood, Glendon, near 

 Kettering, Ponton and Denton, near Grantham. 



In North-West Lincolnshire at Santon Bridge, near to Appleby, a deep road cutting 

 exposes a good section of the lowest beds of Inferior Oolite, reposing upon dark-coloured 

 clays of Upper Lias ; the Midford Sands are altogether absent. The lowest bed of 

 Inferior Oolite is a dark-coloured marly rock only sparingly fossiliferous ; resting upon it 

 is a thick bedded pale brown, hard shelly limestone, containing a numerous and finely 

 preserved series of conchifera; Trigonia hemisphcerica is not uncommon, always as single 

 valves which never attain the dimensions of fully developed specimens in the Cotteswold 

 Hills ; it is accompanied rarely by valves of T. Phillipdi. 



In the same vicinity, higher in position, a small variety of our species (gregaria) occurs 

 abundantly in a large quarry of Lincolnshire Limestone adjacent to the railway station at 

 Appleby ; in size the specimens agree with others from a similar position at the opposite 

 •extremity of the county near to Stamford ; compared with the typical form the Lincolnshire 

 Limestone specimens present some differences, the size measured upon the marginal 

 carina varies from six to fourteen lines, but the greater number are from ten to twelve lines. 



The costae anteally near to the border form a slight undulation, more especially the 

 more umbonal rows ; the area in its surface and carina? has its ornaments less conspicu- 

 ously sculptured. It is difficult to separate specimens of this small variety in a condition 

 suitable for the cabinet, the valves are often in position, but distortion is also common. 

 The first few ill-preserved specimens are mentioned at page 11 in the introductory portion 

 of this monograph as T. gregaria, a name which should be retained only as indicating the 

 present small variety ; figures of which are given upon Plate XXXIII. The matrix, a pale 

 fouff-coloured, tough limestone, is a coralline mud rock, identical in lithological characters 

 with beds which in the Cotteswolds immediately underlie the Oolite Marl, and into which 

 it passes insensibly ; locally they abound in the Cotteswolds with clusters of Nerinoea, 

 Chemnitzia and other univalves, more rarely also with Trigonise, of which the following 

 -seven species have been separated, T. angulata, Sow., T. subglobosa, Lye, T. costatula, 

 Lye, T. pullus, Sow., T. gemmata, Lye, T. Phillipsii, Mor. and Lye, T. tuberculosa, 

 Lye 



At Brough, near Hull, the shelly Inferior Oolite also contains this variety, obtained 

 by Mr. J. F. Walker, of York. 



The testacea of the rock at Appleby consists chiefly of numerous genera and species 

 of Conchifera, almost the whole of which are identical with Cotteswold forms, it is therefore 

 the more remarkable that the Trigonse at the northern locality are represented by a single 

 species of the Costatce, and one of the forms which in Gloucestershire occurs most rarely ; 

 the two quarries, the one Santon, the other at Appleby, together scarcely exceeding fifty 



