PARALLELODON WALCIODORENSIS. 149 



1842 really belongs. This shell is not reproduced in the later work, but entirely 

 new examples are depicted. 



Most of the specimens in the museums in Britain bearing the label " Area 

 Lacordaireana " are narrow elongate forms, easily distinguished from that species 

 by the narrow dorso-ventral measurement. At present I am able to give only one 

 English locality for this species, the shells quoted as belonging to it from other 

 places being distinctly different. On account of the uncertainty mentioned above, 

 I have omitted in the list of synonyms all references made to this species where 

 figures and descriptions are absent. 



The anterior end is much shorter in the specimen which I think may belong 

 to P. Lacordairianus than in those more closely resembling it ; and this fact, 

 taken with the absence of any angularity in the obtuse ridge, great comparative 

 depth (dorso-ventrally and laterally), and the finer ornament of the valves, serves 

 to distinguish it from other species of the genus. But it is possible a larger 

 number of specimens might demonstrate that the shell which I figure is only a 

 variety of the species to be described next. 



Parallelodon Walciodorensis, de Koninch, 1885. Plate X, figs. 11 — 15. 



Parallelodon "Walciodorensis, de Koninch, 1885. Annales Musee Koy. Hist. 



Nat. Beige, vol. xi, p. 161, pi. xxx, figs. 13, 

 27, 28, and 43. 

 ? — tenuistria, de Koninch, 1885. Ibid., p. 162, pi. xxv, figs. 36, 40, 



44; pi. xxvi, fig. 4. 



Specific Characters. — Shell of moderate size, elliptically transverse, relatively 

 very moderately gibbose, but regularly convex. The anterior end small, and some- 

 what compressed. Its anterior superior angle is a right angle, below which the 

 border is semicircularly curved, and passes without break into the inferior border, 

 which is feebly convex in its greater portion, but more so at each extremity. The 

 posterior border is straight and obliquely truncate from above downwards. The 

 posterior inferior angle is bluntly rounded, and is the most posterior portion of 

 the shell. The posterior superior angle is a little greater than a right angle. 

 The hinge-line is straight, and quite as large as the longest transverse diameter of 

 the valve. The umbones are swollen and obtuse, raised above the hinge-line, 

 incurved, and almost contiguous, being separated by an almost linear ligamental 

 area. They are situated in the anterior quarter of the hinge-line. 



The valves are compressed immediately in front and also at the posterior superior 

 angle, above a line passing from the posterior border of the umbo to the posterior 

 inferior angle ; elsewhere they are regularly convex, more so from above down- 

 wards than from before backwards. The greatest convexity is subumbonal. 



