SCALDIA FRAGILIS. 335 



De Koninck lias described ten species as belonging to the genus, retaining six 

 species figured and described by de Ryckholt, but I think it probable that many 

 of them represent only different stages of growth of a species. 



I have not found any species of Scaldia in the rich fossiliferous localities of 

 the Mountain Limestone of England, but the genus occurs in the Carboniferous 

 Limestone series of Scotland, and is represented by one species which I refer to. 

 S.fragilis, de Koninck. In Ireland one species, 8. Benedeni ana, is represented by 

 one specimen in the Museum of the Geological Survey of Ireland from the 

 Limestone of Tuogh, co. Limerick, and two specimens from Kildare in the 

 Museum of the Geological Survey at Jermyn Street, London. Unfortunately, in 

 none of the specimens from these localities is the hinge to be seen. 



I figure, for purposes of comparison, a specimen of Scaldia Lambotteana, from 

 the Tournay beds, PI. XXXVII, fig. 4. This specimen (a left valve) shows the 

 hinge-line with the characteristic single cardinal tooth. As in the more ovate 

 species of Edmondia, this species resembles that genus in possessing a shelly 

 process of the hinge-plate which projects into the umbonal cavity. There is 

 probably a very close relationship between Paracyclas, Hall, 1843, and Scaldia, 

 de Ryckholt, 1852. Hall states iu his diagnosis, " Structure of hinge not fully 

 observed ; ligament supported on each side by a narrow plate, and leaving in the 

 cast two diverging grooves directed forward from the beak." The Devonian 

 shells referred to Paracyclas are flatter and more generally compressed, and much 

 more nearly shaped like Lucina than the Carboniferous shells referred to Scaldia. 

 In the absence, however, of sufficient evidence of the exact structure of the hinge 

 of Paracyclas, it is impossible to say at present that the two genera are 

 synonymous. 



Scaldia feagilis, de Koninch, 1885. Plate XXXVII, figs. 5—7. 



Scaldia fkagilis, de Koninck, 1S85. Ami. Mus, Roy. d'Hist. Nat. de Belgique, 



torn, xi, p. 58, pi. xiv, figs. 3G — 38. 



Specific Characters. — Shell of less than medium size, subcircular, strongly 

 gibbose, slightly inequilateral. The anterior end is deep in the dorso-ventral 

 direction, regularly convex, and its border almost semicircularly curved. The 

 inferior border is convexly curved, and the posterior truncate, forming with the 

 inferior margin a bluntly rounded angle. The hinge-line is curved, and makes a 

 more or less obsolete obtuse angle behind with the posterior border. The 

 umbones are small, triangular, and acutely pointed, incurved, subcentral, and 

 somewhat raised above the rest of the shell. The valves are strongly and 

 regularly convex, especially above. Passing obliquely downwards and backwards 



