MODIOLA MACADAMII. 63 



MoDiOLA Macadamii, Povtlock, 1843. Plate II, figs. 20—22. 



MoDiOLA Macadamii, var. angusta, Portlock, ISIS. Report Geo). Londonderry, 



&c., p. 432, pi. xxxiv, fig. 13. 

 Non — — var. elongata, Portlock, 1843. Ibid., fig. 14. 



— — — var. LATA, Portlock, 1843. Ibid., fig. 15. 



— — Morris, 1843. Catalogue of British Fossils, p. 91. 



— — — MCoij, 1844. Synopsis of the Characters of the Carb. 



Limestone Fossils of Ireland, p. 75, 



— • Brown, 1849. Foss. Conch, p. 175, pi. Ixi***, fig. 14. 



— — — — — Ibid., figs. 15, 16. 



Mttiltjs — de Ryckholt, 1853. Melanges paleontologiques, part 2, 



p. 87. 



— MoDiOLA — Baily, 1875. Figures of Characteristic British Fossils? 



p. 114, pi. xxxix, fig. 6. 



— — Kinalian, 1878. Manual Geol. Ireland, pi. iii, fig. 4. 



— — Picjshy, 1878. Thesaurus Devonico-Carboniferus, p. 309. 



— — var. ANGUSTA, pars, Etheridge, 1888. British Fossils, 



vol. i, PalaBozoic, p. 285. 



Specific Characters. — The shell is small but lengthened, narrow, and convex, 

 and must approach to a cylindrical form when both valves are together. Appa- 

 rently equivalve. The anterior end is almost obsolete, and has a bluntly pointed 

 extremity, moderately convex. The inferior border commences in front by curving 

 downwards from its junction with the anterior, and then becomes straight, making 

 with the hinge-line an angle of about 15° ; then it passes into the posterior 

 border in a bluntly rounded curve. 



The posterior part comprises by far the greater portion of the shell, and is 

 expanded and flattened. Its border is at first obliquely truncate from above 

 doAvnwards and backwards, and then bluntly rounded to meet the inferior margin. 

 The hinge-line is straight, and equal to about half of the greatest length of the 

 shell in extent, forming behind a very obtuse angle with the posterior border. 



The umbones are almost anterior, but apparently not quite terminal ; very 

 inconspicuous. Passing downwards and backwards from the umbones is a very 

 gibbose oblique swelling, which becomes rapidly expanded and lost on the surface 

 of the shell as it approaches the postero-inferior angle, the upper border of the 

 swelling being the more accentuated, above which the shell is at once compressed 

 and expanded upwards. 



The interior has not been observed. 



Exterior. — The surface of the shell Js smooth, but under the microscope very 

 fine concentric lines of growth are apparent. Shell very thin. 



