Counties of Durham and Northumberland. 51 



sinus in the middle, rounded towards the lateral margins ; imper- 

 forated valve high in the middle, depressed torvards the sides ; the 

 front margin of the sinus and sides produced horizontally a short 

 distance from the cavity of the shell ; surface with numerous plaits 

 in the sinus, which are sometimes bifurcated, and a few on the 

 sides granulated." 



This species was first described under the above name in the 

 ' Trans. Tyneside Nat. Field Club/ where also some other pecu- 

 liarities are pointed out by which it may be known and distin- 

 guished from the preceding species. The testimony of von Buch 

 in favour of this opinion is singular, for at the same time that 

 he separates Terebratula Schlotheimi from the T. lacunosa, he 

 expressly says that the latter is found in the magnesian lime- 

 stone at Humbleton. 



It occurs in the shell-limestone at Humbleton, sometimes in 

 considerable abundance. I have never found it at Dalton, nor 

 do I think that it occurs there. I have however taken one spe- 

 cimen from the magnesian conglomerate of Tynemouth. It is a 

 very local species, and has not yet been found, I think, in any 

 foreign locality. 



11. Spirigera pectinifera. Sow. — The internal structure 

 of this very interesting shell is not correctly represented in 

 King^s Monograph, so far as I am able to judge from speci- 

 mens collected at Humbleton. In the enlarged figure, tab. 10. 

 fig. 9, the platform, or expansion between the crura of the 

 loop, is much too large, and in fig. 10 the coil is represented 

 with small blunt pectinations round its outer margin. This 

 serrated appearance is due to mineralization, for upon close 

 examination the entire coil of some examples is found to be 

 covered all over with fine crystals. In the greater number of 

 specimens of the interior that I have seen, the coil appeared 

 quite smooth. For the perfect understanding of this species it 

 will be necessary to consult Mr. Davidson^s excellent plates, 

 Mon. Brit. Perm. Brach. pi. 1. figs. 50-56, pi. 2. figs. 1-5, in 

 which all the peculiarities of this singular shell are carefully 

 represented. I have not however, up to the present time, been 

 able to detect the presence of spinous processes on the margin 

 of the coil. 



In England this species is almost as limited in its distribution 

 as the last, occurring only in the shell-limestone at Humbleton, 

 Tunstall and Hylton, and in the magnesian conglomerate at 

 Tynemouth. 



12. Martini A Clannyana, King. — This species does not 

 appear to be covered with spines, as some have supposed, but 

 the outer surface of the valves is studded all over with minute 

 granulations. 



4* 



