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BRITISH FOSSIL TRIGONLE. 



Greensand possess similar features and reduce the supposed examples of T. Archiaciana 

 to the little moulds exemplified, PI. XXV, fig. 16, from the Upper Greensand of the 

 Isle of Wight and of Warminster; these are, however, altogether ill preserved and 

 doubtful as examples of that species. See also p. 141. 



I am also inclined to regard our specimens of T. Vicaryana as identical with the 

 T. spinosa of D'Orbigny, which that author mistook for the T. spinosa of Parkinson and 

 of Sowerby ; no figure has been given of T. Pyrrha, D'Orb., but the few words of 

 description agree with the T. spinosa of British authorities. 



Trigonia sign ata, Ag. Page 29, Plate II, figs. 1, 2, 3. 



In the description of this species, p. 29, no allusion was made to the figure of T. 

 davellata in the work of Knorr (' Verst./ vol. ii, pi. B, fig. 1 a ; 1775), which was referred 

 to by Agassiz as one of the types of his T. signata ; this omission resulted from a lack of 

 confidence in an engraving of one of the Clavellatcs in a work of such considerable 

 antiquity. 



The figures of T. davellata in Zieten's ' Die Versteinerungen Wiirtembergs' are 

 also quoted by Agassiz as one of his types of T. signata ; and, as they are free from 

 the objection above referred to, and also agree generally with British Inferior Oolite 

 specimens within slight limits of variation, and as the number of specimens collected 

 within the last thirty years from Yorkshire, Oxfordshire, and Gloucestershire are very 

 considerable and all approach nearly to Zieten's type, I preferred to regard the latter as 

 the species intended by Agassiz. 



In this arrangement we should regard the figure given by Agassiz, 1 Trig.' pi. ix, 

 fig. 5, as a variety, excluding his pi. iii, fig. 8, which represents a specimen very defective 

 in condition and doubtful as a species. The example given in ' Trigonies,' pi. ix, fig. 5, 

 is apparently founded upon Knorr's figure, and differs as a variety from the figures by 

 Zieten ; it is remarkable for the much greater upward curvature given to the posteal 

 portions of the costse, which are also more attenuated ; the same feature equally charac- 

 terises the imperfect specimen figured by Devvalque and Chapuis, ' Pal. Luxemb.,' p. 172, 

 pi. xxvi, fig. 1. As the two figures (Knorr's aud Agassiz') above mentioned differ from 

 all the known British specimens, and the latter have a general unity of aspect and 

 accordance with Zieten's figures, I have adopted the last for the type of T. signata. 



The description at p. 29 sufficiently records the differing positions in the Inferior 

 Oolite in which the species has occurred ; it may, however, be mentioned that the 

 Upper Trigonia-grit of the Cotteswolds has supplied the specimens having the growth 

 most fully developed, and that in such the rows of costae anteally sometimes become 

 irregular and confused ; in specimens from other positions in Oxfordshire and Yorkshire 

 the rows of costae are remarkable for their regularity and uniformity. 



