GASTEROPODA. 61 



Specimens, as small as the head of a pin, are scattered over the blocks of white stone 

 at Bussage, and planking at Minchinhampton Common — these are smooth. The larger 

 shells are more distinctly snlcated, and occasionally attain a diameter of three eighths of 

 an inch. 



Locality. It occurs in all the shelly beds at Minchinhampton; at Ancliff, in Wiltshire; 

 and at Charter House, Hinton, Somersetshire. Langrune, France. 



Family — Tu rb i n i dm . 



Trochus, Linnaus, 1758. 



Shell turbinated, conical ; spire elevated, consisting of numerous whorls; under surface 

 discoidal ; aperture more or less depressed obliquely, entire, generally angular ; columella 

 curved, more or less prominent at its union with the outer lip, contiguous to the axis of 

 the shell. 



The fossil species of the Great Oolite are all very small, and are tolerably numerous in 

 the shelly beds. 



Trochus Dunkeri. Plate X, figs. 3, 3a. 



T Testa conicd, glabra; anfractibus laviyatis et planis (4 — 6); apice acuto; aperturd 

 obliqitd, umbilico nullo. 



Shell conical, smooth; whorls very smooth and flattened; apex acute; aperture oblique; 

 no umbilicus. 



The extreme flatness of the whorls, and moderate elevation of the spire, are the chief 

 features ; the good specimens have oblique lines of growth upon the last whorl, near to 

 the aperture. 



Locality. This little species is tolerably abundant in the white stone of Eastcombs 

 and Bussage. 



Named after Dr. W. Dunker, Professor at the Polytechnic School of Cassel. 



This species has some affinity with the Trochus ylaber, Koch {Gold/. Pet. t. 1796. 12); 

 but the volutions are striated and the base more convex. 



Trochus plicatus, Archiac. Plate X, figs. 8, 8a. 



Trochus plicatus, Archiac. 1843. Mem. Soc. Geol. France, vol. v, p. 379, t. 29, fig. 5. 

 _ _ D'Orb. 1850. Prod. Paleont., p. 300. 



— — Bronn. 1848. Index Palseont., p. 1304. 



9 



