278 NOTES ON THE PERMIAN SYSTEM OF 



wliorls to a double keel inclines me strongly to think tliat tlie 

 Murchisonia stihangulata, Geinitz, is only the same shell ; and it 

 is also very prol>able that the original Russian species, Tiirritella 

 biwriiica, Kut., and M. siihangulata, Yern., are identical with the 

 present species. Some of Mr. Kirkby's specimens also show two 

 or three coloured sjoiral bands running round the whorls parallel 

 to the suture, as figured by Mr. King in the " Perm. Mon." 



It occurs in the shell-limestone of this district, chiefl}^ at 

 Tunstall. 



32. LITTOEINA, Fenissao. 



1. L. HELiciNA, Schloth. sp. PI. XL figs. 19, 20, vars. 



Most authors describe the typical form of this species as 

 having only three or four whorls, yet all the best full-grown 

 specimens have five or six. The nucleus of the shell and the 

 succeeding whorl are quite smooth, and in a few instances this 

 smoothness is continued through the whole period of growth. 

 This variety is termed Rissoa obtiisa, Brown, and Turbo Permi- 

 amis, Kin^. Generally, in the typical L. helicina, after the 

 first two or nucleal whorls, the shell begins to be ornamented 

 with more or less numerous, much or slightly developed strise 

 running parallel with the suture, which are fewer, stronger, and 

 more prominent on the middle, and fainter and more numerous 

 on the lower part of the whorl. The spire also in some instances 

 is much drawn out, in others much depressed, causing the body- 

 whorl to appear in the latter case much larger than usual. The 

 ornament of the shell has sometimes the form of flattened, an- 

 gulated planes over the upper part of the whorls, which are in a 

 few instances so obscure as to be scarcely perceptible (see PI. XL 

 figs. 19, 20), and it is thus that the typically ornamented forms 

 are united w^ith the smooth variety above mentioned. I can find 

 no character by which to distinguish the Turbo 3Iancumensis, 

 Brown, from this, which certainly is identical with typical spe- 

 cimens of Trochilites helicina, Schloth.. received from Germany. 

 A glance at the figures in the " Perm. Mon." tab. 16, f. 19- 

 22, is sufficient to convince any sound naturalist of the identity 

 of helicina and Mancnniensis. 



