Counties of Durham and Northumberland. 305 



Schauroth at Poessneck; and some examples kindly sent me for 

 comparison agree with ours in every particular. 



It differs from the preceding chieiiy in the obliquity of the 

 valves, in the narrowness of the hinge-hne, and the more tri- 

 angular appearance of the area. It has also no byssal notch. 

 The surface, in perfect specimens, is ornamented with tine par- 

 allel lines of growth, and small radiate depressions run from 

 the umboues to the margin. For the present, it may be left in 

 the genus Limn, but this requires further examination. 



In the shell-limestone of Tunstall and other localities ; not 

 very common. 



18. MoNOTis SPELUNCARIA, Schloth. — Certainly no one at 

 all conversant with this pre-eminently characteristic Permian 

 bivalve can assent to its being unnecessarily broken up into 

 three species, as proposed by the author of the ' Perm. Mon.^ 



As pointed out in the Tyneside Catalogue*, the convex 

 valve when perfect exhibits " a few strong, imbricated or granu- 

 lated diverging ribs, between which there are others much finer 

 and closer together." The granulations are strongest on one 

 side of the valve, and occur only on those specimens that are of 

 very regular growth. On the coarser and larger individuals the 

 ribs are covered with strong imbricating processes, which are 

 oftentimes considerably produced. These characters correspond 

 with those given by Dr. Geinitz in his ' Versteinerungen,^ but 

 Avicula Kasanensis,Geimtz, 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. 



19. Gervillia antiqua, Munst. = G. inflata, Brown, sp. — 

 At present 1 am unable to decide which of the above names 

 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. ceratophaffa. Many other 

 eminent naturalists also are of opinion that antiqua is only a 

 variety of the latter ; but I am not at liberty at present 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 



* Through an unfortunate oversight, an erroneous date was given to the 

 pubUcation of this Catalogue in a former number of the ' Annals.' Instead 

 of Aug. lOth, read Aug. IJth, 1848. 



Ann. ^ Mag. N. Hist. Ser. 2. Vol. xix. 20 



