PARALLELODON TENUISTRIA. 151 



Parallelodon tenuisteia, M'Coy, sp., 1844. Plate XI, figs. 1 — 4 a. 



Cucull^a tenuistria, M'Coy, 1844. Synopsis Carb. Toss. Ireland, p. 72, pi. xii, 



fig. 10. 

 Aeca Maccotana, de Koninck, 1851. Supplement Anim. Foss. Carb. Belg., 



p. 670, pi. lvii, figs. 8 a— c. 

 CuctjlLjEa tenuistria, Morris, 1854. Cat. Brit. Foss., p. 197. 



Griffith, 1860. Journ. Geol. Soc. Dublin, vol. ix, p. 92. 



— tenuistriata, Bigsby, 1878. Thesaurus Devonico-Carbonif'erus, p. 305. 



— tenuistria, Etheridge, 1885. Brit. Foss., part 1, Palaeoz., p. 282. 



? Parallelodon tenuistria, de Koninck, 1885. Ann. Musee Roy. Hist. Nat. 



Beige, p. 162, pi. xxv, figs. 36—40, 44 ; pi. xxvi, 

 fig. 4. 

 Non Macrodon tenuistriatus, Meek and Worthen, 1867. Proc. Chicago Acad. Sci., 



vol. i, p. 17. 

 — — — Meek, 1872. U. S. Geol. Surv. Final Report Nebraska, 



p. 207, pi. x, figs. 20 a, I. 



Specific Characters. — Shell transversely oblong, subcylindrical. The extreme 

 anterior end compressed, but elsewhere, except on the dorsal slope, the valves are 

 regularly convex and gibbose. The anterior end is short ; the anterior superior 

 angle projects forwards, below which the border is semicircularly curved, and 

 so passes into the inferior border. This is convex in front, slightly so in its 

 median portion, and almost straight posteriorly, but directed somewhat upwards. 

 The posterior border is narrower than the greater portion of the shell, truncate 

 from above downwards and somewhat backwards, and almost straight, making an 

 obtuse angle above with the hinge-line, and a rounded obtuse angle below with 

 the inferior border. The hinge-line is straight, and equals the longest diameter 

 of the shell. The umbones are small, gibbose, approximate, slightly raised above 

 the hinge-line, and situated in the anterior fourth of the hinge-line. The ligamental 

 area is narrow and elongate. The valves are flattened at the anterior superior 

 and posterior superior angles ; elsewhere they are regularly swollen from before 

 backwards, and above downwards. The posterior slope is comparatively narrow 

 and hollowed out, but not bounded below by a ridge. 



Interior. — The muscle-scars are normal in situation, but very indistinct and 

 shallow. The pallial line is entire and remote from the margin. Of the hinge- 

 plate I am only acquainted with the anterior portion, which is similar to that in 

 the other species of Parallelodon. 



Exterior. — The surface is ornamented by regular, fine, radiating strias, which 

 become more marked as they approach the inferior border, being almost invisible 

 to the naked eye near the umbones. 



