140 CARBONIFEROUS LAMELLIBRANCHIATA. 



totally different species of the same genus, and I am unable to decide on the 

 priority in this case ; but fortunately the reference of the Palseozoic Areas to 

 Parallelodon permits the retention of de Koninck's original specific name. 



The only British specimens which I have been able to examine are 

 unfortunately all incomplete posteriorly ; consequently I have been compelled to 

 follow the description of this part of the shell as given by de Koninck, who states 

 that the posterior border is shorter than the anterior, owing to the rapid upward 

 curvature of the posterior part of the inferior border. 



De Koninck figures two specimens of P. sqiiamosus in his later work, which 

 are the extreme terms of variation in a species which he describes as very variable 

 (p. 156), " Bile varie entre celle representee, pi. xxiv, fig. 44, et celle de la pi. xxv, 

 fig. 15, que j'avais d'abord considered comme specifiquement differente, mais que 

 se relie a la premiere par des specimens intermediares." 



On the same page (p. 156) he proceeds to describe the specimen figured on his 

 pi. xxv, fig. 15, as a new species, under the name of P. undatus, of which he says, 

 " ce Parallelodon ressemble au P. fimbriatus par les plis de sa surface qui sont 

 cependant plus minces et plus lamelleux ; et en differe considerablement par sa- 

 petite taille et par sa forme relativement beaucoup plus allongee." 



I have been fortunate enough to isolate the greater part of the hinge in a 

 specimen (PI. IX, fig. 22, of which 22 a is an enlarged drawing) in the Burrow 

 Collection of the Woodwardian Museum, Cambridge, which, with others of this 

 species, I am permitted to figure by the kindness of Professor McKenny Hughes. 

 Two other specimens are in the Collection of the Geological Survey, Jermyn 

 Street, from the Carrington Collection, one of which, PL IX, fig. 18, is figured ; 

 and these, with one other from Hill Bolton, near Grassington, in my own collection, 

 are all the specimens of this species that I have any knowledge of. It is, therefore, 

 probably very rare. 



Parallelodon corrugatus, de Koninck, 1885. Plate X, figs. 16 — 19. 



Paballelodon coeeugattts, de Koninck, 1885. Ann. Musee E. Hist. Nat. Beige, 



vol. xi, p. 160, pi. xxv, figs. 1, 2. 



Specific Characters. — Shell of moderate size, subrectangular, and gibbose. The 

 anterior portion of the shell is compressed and narrowed. Its border is rounded 

 above, forming an obscure lobe at the anterior superior angle ; it then descends 

 downwards and inwards, becoming semicircularly curved into the inferior border, 

 which is almost straight, but markedly sinuated at the junction of the anterior 



