ANTHRACOMYA MODIOLARIS. 97 



Whitley, Newcastle and Durham Coal-field ; Grain's Ironstone, South Stafford- 

 shire ; Stubb's Mine, Bardsley. South Wales Coal-field : Sychffos ; Darren Pins, 

 Aberdare. Scotland : Splint Coal, Shettleston, Ardrie, and Larkhall ; Annandale, 

 Kilmarnock, Old Cummock, Ayrshire, — all in the Upper and Middle Coal-measures. 



Observations. — Owing to the fortunate preservation of the types of this shell 

 and the specimen subsequently figured by Salter, I have been able to reproduce 

 them by the kindness of Prof. Prestwich and of Sir A. Geikie, Director-General 

 of the Geological Survey, and with the exception of two synonyms invented by 

 Captain Brown and a mistaken reference by myself this shell has always been 

 recognised by authors. I figure these shells from Prof. Prestwich's Coalbrookdale 

 Collection on Plate XVI, figs. 49 and 50 representing the two specimens 

 figured by Sowerby (op. cit. supra) as his fig. 10. I judge from measurements, 

 and from the fact that Prof. Prestwich has marked both specimens as figured, that 

 the two figures numbered 10 in the ' Geology of Coalbrookdale ' are from 

 different specimens, one showing the view from above, the other and larger one 

 from the side. These are both more elongate than Mr. Salter's form, and have 

 the dorsal and ventral margins more nearly parallel ; but with these in Prof. 

 Prestwich's Collection is a shell from the same locality figured on PI. XVI, 

 fig. 51, which is almost identical in form with Mr. Salter's shell, showing that in the 

 young the shell had a more triangular shape. I produce on PI. XIII, fig. 9, the 

 shell which was the original of Mr. Salter's figure in the ' Geological Survey 

 Memoir on the Iron Ores of South Wales.' This is also a cast, but it shows no 

 muscle-scars, except the anterior adductor very faintly on the left side. 



From the series figured from North Staffordshire it will be seen that the 

 shape and degree of acuteness of the oblique ridge is very variable, and also the 

 amount of expansion upwards of the posterior part of the hinge-line. This may, 

 I think, be due to the fact that the types are all casts, and that the thin part of 

 the valves which came absolutely into contact with each other would therefore not 

 be indicated in casts. All the shells, it may be noted, which have this character 

 possess more or less shell-structure preserved. Thus fig. 10, PI. XIII, and 

 figs. 1, 7, and S, PI. XIV, all show the posterior part of the hinge-line expanded 

 upwards. 



1 have been fortunate enough to obtain a nearly perfect example of the hinge 

 of this species, only the extreme anterior and posterior positions being wanting. 

 This specimen, which is figured on PI. XVI, fig. 52, came from the same bed at 

 Whitley, Northumberland, where Prof. King obtained the hinge-plates on which 

 he^ founded his o- e nus Anthracosia, and shows a characteristic posterior lateral 

 tooth, and a small cavity under the umbo, probably to receive a cardinal tooth of 

 the opposite valve. 



Whether these conditions obtain in other species is at present unknown. 



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