﻿QUADRATE. 



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Siratiyraphical position and Localities. — T. nodosa constitutes two varieties in 



Britain, the differing characters of which may be stated synoptically as follows : The 



typical form. — Area forming a moiety of the surface of the entire valve; nodes of the 

 marginal carina small and regular in figure, size, and arrangement ; rows of pallial 

 varices regular, without bifurcations, and becoming attenuated near to the border. 

 Position. — Perna bed at Redcliff, Sandown Bay, Isle of Wight. Hythe, dark grey 

 sandstone bed with T. ornata. Maidstone, Molluskite bed. Tealby, brown pisolite bed. 

 Variety Orbignyana. — Surface of the area never exceeding two fifths of the entire valve ; 

 nodes of the marginal carina unequal in size and irregular in figure and arrangement ; 

 rows of pallial varices variable in figure and arrangement, at the border either large and 

 simple or bifurcating and attenuated, the nodes either distinct or crowded. Position. — 

 The Cracker beds at Atherfield, Isle of Wight; rarely in the Perna bed at Redcliff, near 

 Sandown. 



History, affinities, and comparisons with allied testacea. — For specimens illustrative of 

 T. nodosa from the Neocomian sandstone quarries near Hythe, which was the locality of 

 the type-specimen figured by Mr. Sowerby, I am indebted to Mr. Mackeson, of that 

 place, who, in compliance with requests from Rev. T. Wiltshire and myself, obtained several 

 examples ; these are obscure moulds of external casts in coarse sandstone. Mr. Mackeson 

 had also the good fortune to procure upon a slab of sandstone two external casts of 

 uncompressed specimens ; these have afforded good reproductions of the shell by the aid 

 of gutta-percha pressings, and are found to agree with the form procured at Lympne and 

 in the Perna bed at Redcliff, Sandown Bay. I have also been favoured with information 

 respecting the condition of the species in the quarries of Kentish Rag near Maidstone, in 

 a communication from Mr. J. Bensted, jun., the son of the proprietor of the quarries, 

 whose intelligent remarks I have pleasure in quoting. " It is not uncommon in the 

 Iguanodon quarries, and is found principally in one particular bed of sandstone called 

 Molluskite bed, but simply as a faint white mark formed by the lime of the original 

 shells, which are quite valueless as specimens. I have a single specimen only, which 

 owes its preservation to the fact that the space occupied by the shell appears to have been 

 filled with flint, which was to a certain extent able to resist the pressure which squeezed 

 the others flat." The same gentleman also favoured me with a drawing of the fossil 

 which demonstrated its identity as a species with the gutta-percha pressings from Hythe, 

 the specimen from Tealby, and those from the Perna bed at Redcliff ; from the latter 

 locality the Royal School of Mines has a large specimen, presented by Dr. Fitton, as an 

 example of T. dcedalea, but as the surface of the area is ill-preserved it is not fitted for 

 the artist. 



Upon the same plate with the fragment figured by Parkinson for his T. dcedalea 

 ('Org. Rem.,' vol. iii, pi. xii) is another more doubtful fragment, to which he attached 

 the name of T. rudis ; it supplies a warning example of the impropriety of publishing 

 such materials when no satisfactory description can possibly be founded upon them. 



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