142 CARBONIFEROUS LAMELLTBRANCHIATA. 



in the Burrow Collection in the Woodwarclian Museum of Cambridge, and I am 

 indebted to the authorities for permission to figure and study their specimens. 



Fig. 16, PL X, gives a fair idea of the general shape of the shell and the 

 characteristic markings of the external surface. It also shows, owing to a 

 removal of the posterior part of the test, the posterior adductor muscle-scar and 

 the entire pallial sinus. 



Fig. 17, PI. X, shows the large ligamental area and the hinge-line; though, 

 unfortunately, owing to the fact that the specimen probably had been much rolled 

 before it was embedded, details of the hinge are almost absent. There seem to 

 be some obscure crenulations, just anterior to the umbo, which may indicate 

 teeth ; and the thickening of the anterior and posterior ends of the hinge-plate 

 seems to show that they once bore the teeth characteristic of other shells of this 

 genus. 



Figs. 18 and 19, PI. X, are younger forms, but show the external folds and 

 sulci very plainly. 



De Koninck thought that the species under description came nearer to P. 

 (Byssoarca) reticulatus (M'Coy), which also possesses a large ligamental area; but 

 in this species the radiating strise are much more marked, and the transverse 

 markings are fine, narrow, and more numerous. P. corrugatus appears to occupy 

 a position between P. Verneuilianus and P. reticulatus. 



Parallblodon eeticulatus, M'Coy, sp., 1844. Plate IX, figs. 23 — 25 a ; Plate X, 



figs. 1—4 ; Plate XII, fig. 1. 



Byssoaeca eeticulata, MCoy, 1844. Synopsis Carb. Foss. Ireland, p. 73, pi. xii, 



fig. 9. 

 ? Lanistes eugosus, M'Coy, 1844. Ibid., p. 76, pi. x, fig. 8. 

 CxrcuLL-EA reticulata. Brown, 1849. Ill us. Foss. Concb., p. 193, pi. lxxviii, 



fig. 13. 

 Aeca eeticulata, d'Orbigny, 1850. Prodrome de paleontol., vol. i, p. 134. 



— — Bigsby, 1875. Thesaurus Devonico-Carbonif'erus, p. 299. 



— — Etheridge, 1885. British Fossils, part 1, Palaeozoic, p. 280. 



Specific Characters. — Shell transversely oblong, trapezoidal, moderately gibbose. 

 The anterior end is short, convexly swollen, and its border is straight above, 

 semicircularly curved below, where it passes uninterruptedly into the inferior border. 

 The latter is long and almost straight, and parallel to the cardinal border, but 

 becomes curved upwards at its posterior end to join the posterior border. The 



