NORTHUMBERLAXD AND DURHAM. 201 



oftentiraes considerably produced. These characters correspond 

 with those given by Dr. Geinitz in his " Verstcinerungen," but 

 Avicula Kasanensis, Geinitz, can only be reckoned a coarser 

 variety of this species. 



It is not common in the compact-limestone, but sometimes 

 occurs very plentifully in the shell-limestone of Humbleton and 

 other localities. In the higher deposits it has never been known 

 to occur. 



1(1, GERVILLIA, Brfmnee. 

 1. G. ANTiQUA, Milnst. 



At present I am unable to decide whether the above name 

 ought to be retained for this species, as the figures given by 

 Goldfuss are not very good representations of it, and are referred 

 by Dr. Geinitz to the following, G. ceiritopJiaga. Many other 

 eminent naturalists also are of opinion that antiqna is only a 

 variety of the latter ; but I am not at liberty to adopt this opinion . 



It is altogether a very much broader and a more inflated shell 

 than the following species. The posterior margin is never so 

 much arcuated or forked, and the wings are never so strongly 

 and distinctly marked off from the body of the shell as they are 

 in G. ceratophaga. The cartilage-pits, generally three or four 

 in number, are, from increasing in width with the growth of the 

 hinge-margin, rather triangular, and are placed directly across 

 the area. They are never oblique in the specimens I have ex- 

 amined, as represented in the " Perm, Mon.," and the first pit 

 invariably stretches directly between the umbones. In the 

 clumsily-grown twm'da, which is only a stunted form of this 

 species, they are placed closer together and are more numerous, 

 though the hinge-line is much shorter. The Bakevellia carinata, 

 King, is only the young of the present species, which has often- 

 times two strong, raised, diverging lines running from the um- 

 bones to each side of the byssal notch. 



Through the kindness of Mr. Binney I have made the follow- 

 ing notes on Capt. Brown's species of Avicula from the Lanca- 

 shire Permian deposits: — 



" The three specimens of Avicula Binneyi belong undoubtedly 



VOL. III. PT. IV. 1 I 



