ANIMALS. 207 



Diagnosis. — Three sixteenths of an inch in height, and two sixteenths in width : 

 spire elevated : marked with numerous thread-hke hnes : aperture orbicular. 



IWho Thomsotiianus resembles T. Mancuniensis in form ; but it is a smaller species, 

 and its whorls are marked with numerous spirally-arranged thread-like lines, — not 

 ridges. It has been ornamented with transverse coloured bands. 



This species is of rare occurrence in the Shell-limestone at Tunstall Hill, and in 

 the Breccia at the north end of Black Hall rocks. 



Turbo Taylorianus,^ King. Plate XVI, figs. 25, 26. 



Diagnosis. — As wide as it is high : tumid : marked with numerous thread-like 

 lines: aperture orbicular : spire depressed. 



This species differs from the last in being decidedly more tumid ; both agree, 

 however, in possessing numerous fine spirally-arranged striae. It stands in the same 

 relation to Turbo Thomsonianus as T. helicinus does to T. Mancuniensis. My largest 

 specimen is three sixteenths of an inch in height, and the same in width. 



Turbo Taylorianus occurs at Tunstall Hill, and Humbleton Quarry, in Shell-lime- 

 stone. 



The following ten species have a very doubtful connexion with the genera in which 

 they are placed ; and most of the genera themselves are equally as doubtful as regards 

 the families to which they belong. 



Genus Rissoa, Freminville and Desmarest, 1814. 



Being unacquainted with the original diagnosis, and the typical species of this 

 genus, I am compelled to waive all remarks on it, merely referring the reader to the 

 generic character and observations of the group by Mr. Searles Wood, in his ' Mono- 

 graph of the Crag Mollusca,' part i, p. 100. 



RissoA OBTUSA, Brown. Plate XVI, fig. 18. 



(?) Smooth shell, Sedgwick. Trans. Geol. Soc. Lond., 2d series, vol. iii, p. 118, 1829. 

 (?) Turbo (?), Phillips. Loc. cit. 



Rissoa obtusa, Brow?t. Trans. Manch. Geol. Soc, vol. i, p. 64, pi. vi, figs. 19-21, 1841. 



^ Named after the late Mr. John Brough Taylor, F.S.A., of Sunderland, who intended publishing a 

 work descriptive of "the limestone strata on the coast" of Durham, and "of the extraneous substances 

 deposited in them." (Vide Surtees's History of Durham, vol. i, p. 236.) 



