. PARALLELODON HAIMEANUS. 163 



specimens he remarked (op. sup. cit.), " souvent les cotes rayonnantes dispa- 



raissent si completement que Ton pourrait croire que Ton a affaire 



a une espece differente." 



P. fallax resembles P. decussatus more nearly than any other species, but it is 

 very easily distinguished from the latter by its square form, and the projecting 

 anterior-superior angle. It seems to have never attained the dimensions of 

 P. decussatus. De Koninck states that the ornaments of the surface in P. fallax 

 resemble those of P. Haimeanus, but the latter species is only described in the 

 earlier work, and I do not see the least similarity in the markings of the two 

 species, as will be seen on comparing the figures of P. fallax with those of 

 P. Haimeanus on PI. XI, figs. 23 — 31. 



In the original description de Koninck contrasts the species with A. Maccoyana 

 (P. decussatus, M'Coy) and A. anatina (P. tenuistriatus, M'Coy). The latter is a 

 much more transverse shell and of much larger growth, and I do not think that, 

 although the surface-markings are very similar, the two forms are different states 

 of growth or even varieties of the same species. 



The series of samples from Settle in the Woodwardian Museum at Cambridge 

 are very fine and perfect examples, PI. XI, figs. 23, 25, and 26. It appears that 

 the radiating striae are much better marked in young examples, and become 

 gradually obsolete with adolescence. 



The shell, fig. 24, PI. XI, from the Geological Survey Collection, Jermyn 

 Street, shows the details of the interior very well. The hinge-plate behind is 

 perfectly seen, but in front it is difficult to accurately make out the teeth. 

 De Koninck states that there are four anterior teeth, and shows them in his 

 original drawing of A. anatina (op. supra cit.). 



Parallelodon Haimeanus, de Koninck, sp., 1851. Plate XI, figs. 29 — 31; Plate 



XIII, fig. 8. 



Aeca Haimeana, de Koninck, 1851. Anim. Foss. Terr. Carb. Belgique, Supple- 

 ment, p. 672, pi. lvii, figs. 9 a — c. 

 — Bigsby, 1878. Thesaurus Devonico-Carboniferus, p. 299. 



Paeallelodon multilineatus, de Koninck, 1885. Ann. Musee Hist. Nat. Beige, 



vol. xi, p. 144, pi. xxi, figs. 16 — 18. 



Specific Characters. — Shell compressed, expanded, suborbicular, somewhat 

 oblique. The anterior part of the shell is compressed, and the narrowest portion 

 of the shell is in the dorso-ventral direction. Its border is an elliptic curve, 

 and passes into the inferior border without a break. The latter is curved at each 

 extremity, but in the median portion is almost straight. It is directed downwards 



