Vol. 67.] EAUNAL HORIZONS IN THE BRISTOL COALFIELD. 331 



the thin, much wrinkled periostracum which overlies them, the 

 wrinkling of the latter diverging in every direction. 



Young individuals are much less oblique than older forms, and 

 have a somewhat rounded quadrangular outline. 



A number of beautifully preserved specimens were obtained from 

 the Upper Series of the Upper Coal-Measures of Radstock. They 

 serve to show that the roughly quadrangular form which this 

 species possesses when young is also retained in adult age if the speci- 

 men be well preserved, and further that the shell is strongly tumid. 

 A few examples were found in well-bedded Lower Coal-Measure 

 black shale at Speedwell Colliery. There is no little difficulty in 

 separating this form from Anthracomya Icevis var. scotica : the latter 

 is, on the whole, not so robust a species, and is more broadly 

 ovate. 



Horizons and localities. — At Horizons 1, 2, and 3 below 

 the Bedminster Great Vein, Lower Coal-Measures, South Liberty 

 Colliery, Bristol ; in black shale, Lower Coal-Measures, Speedwell 

 Colliery, Kings wood ; in the roof-shales of the Eock or Badger 

 Yein, Second Series of the Upper Coal-Measures at Writhlington 

 Colliery, Radstock ; spoil-heap at Tyning Batch, Radstock ; in the 

 Second Series of the Upper Coal-Measures at Foxcote Colliery, 

 Radstock. 



Naiadites elongata Hind. (PI. XXVII, fig. 14.) 



A series of uncrushed and well-developed examples of this species 

 were found at Horizon 2, in the Lower Coal-Measures at South 

 Liberty Colliery. The resemblance, as they lay in the shale, to 

 Anthracomya minima was extremely close ; but subsequent libera- 

 tion of one entire specimen showed conclusively that it belonged 

 to Naiadites. Dr. Wheelton Hind 1 has already noted this close 

 superficial resemblance. The shell is markedly tumid in both 

 valves, transversely elongated, and would be somewhat modioliform 

 were it not for the well-developed posterior angle of the hinge-line. 

 Only the faintest trace of lines of growth can be distinguished. 

 Several of the specimens occur in a compact brown ironstone. 

 From the roof-shale of the High Vein at Coalpit Heath was 

 obtained the greater part of a right valve. It occurred in black 

 shale charged with plant-remains, and in association with Leaia 

 leidyi var. salteriana. As the valve is uncrushed, the Antliracomya- 

 like appearance is well shown, and indeed there is nothing 

 externally evident which would remove this species from that genus. 

 A finely-preserved left valve from Radstock has come into our 

 possession. Like all the rest, it is markedly tumid. 



Horizons and localities. — Horizon 2 below the Bedminster 

 Great Vein, Lower Coal-Measures, South Liberty Colliery, Bristol ; 

 roof-shales of the High Vein at Coalpit-Heath Colliery, Coalpit 

 Heath ; shales over the Rock or Badger Vein in the Second Series 

 of the Upper Coal-Measures, Writhlington Colliery, Radstock. 



1 • Carbonicola, Anthracomya, & Naiadites ' Pal. Soc. Monogr. (1894-96) 

 p. 143. 



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