468 Mi\ R. Howse on the Permian System of the 



In addition to the characters given above under Turritella 

 Phillipsii, it may be stated that in very many specimens the 

 whorls are very much flattened or bevelled, both above and be- 

 low, causing a deep suture, and the middle part of the whorls 

 to appear as if doubly keeled. In some few specimens, indeed, 

 there are indications of obsolete spiral striae, and Mr. Kirkby 

 has collected one specimen in which the last two whorls have 

 several very strong spiral strise, though the other whorls have 

 the smooth normal appearance only. This tendency of the 

 whorls to a double keel inclines me strongly to think that the 

 M7i7'chisonia subangulata, Geinitz, is only the same shell ; and it 

 may also happen that the original Russian M. subangulata, \e,vn., 

 is identical with the present species. Some of Mr. Kirkby's 

 specimens also show two or three coloured spiral 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, chiefly at Tun- 

 stall. 



38. LiTTORiNA HELiciNA, Schloth. sp. PI. IV. 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 obtusa, Brown, and Turbo Permi- 

 anus, King. 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 stria3 

 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. IV. 

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

 are united with the smooth variety above mentioned. I can find 

 no character by which to distinguish the Turbo Mancuniensis, 

 Brown, from this, which certainly is identical in its common 

 form with typical specimens of Trochilites helicina, Schloth., re- 

 ceived 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 Mancuniensis. 



The form which was separated under the epithet L. Tunstall- 



