A. a. Hunt — Devonian Hocks of South Be ton. 341 



species and T. (?) trigonostoina, if we may judge from Hall auJ 

 Whitfield's figure, which exhibits the discoid spiral region wedged 

 in between the apertural lips, in other respects the American 

 species diifers in being deeply sinuate, and possessing no perforations. 

 In making an examination of the Silurian Gastropods in the 

 Jermyn Street Mnseum, through the kindness of my former col- 

 league, Mr. George Sharman, the Palseontologist, my attention was 

 directed to three specimens, on a tablet nmnbered y|, from the 

 Lower Ludlow of Mary Knoll, all of which were referred to 

 B. dilatatus, though probably only one of them could with safety 

 be referred to that species. One of these three specimens had a wide 

 umbilical region, as well as some raised prominences on the central 

 part of its dorsal surface, strongly suggestive of perforations, and 

 in other respects the specimen appeared to closely resemble the 

 genus Trematonotus. 



EXPLANATION OF PLATE IX. 

 Fig. 1. Trematonotus Britannlcus, E. B. Newton. Ventral view. 

 Fig. 2. Dorsal view of same specinien ; the dotted outline indicates the extent of 



expansion which is hidden by matrix. 

 Fig. 3. Profile of same exhibiting the reflected lip and the raised perforations. 

 Fig. 4. Dorsal view of another specimen with fewer orifices. 

 The figures are drawn of the natural size. 



IL — On certain Affinities Between the Devonian Kocks of 



South Devon and the Metamorphio Schists. 



(Part III.) 



By A. E. Hunt, M.A. 



{Concluded from page 294.) 



The Intensity of the Metamorphio Action. 



IN the Devonian sandstones and grits of Torbay abundant quartz 

 veins are occasionally developed, indicating a moderate amount 

 of heat. Neither the quartz-grains nor occasional fragments of felspar 

 are to any extent affected. 



At Dartmouth, on the raised-beach platform, quartz is largelj'^ 

 developed together with a little felspar and chlorite, indicating 

 sufficient heat to form or re-form these minerals. At Slapton Sands 

 the grits are about the same as in Torbay : felspar granules remain 

 angular and intact. 



Between Beesands village and Tinsey Head the quartz-grains 

 occasionally show signs of incipient solution, as also do the tour- 

 malines. In one slide (No. 5) the approach of schistosity seems to 

 he heralded by minute roughly parallel cracks cemented by iron 

 ores and a pale-green mica.^ Minute crystals of pyrites, some 

 rectangular, are formed in the rock. At the Start, in rare cases, 

 grains or remnants of grains of original granitic quartz can he 

 detected in the schist.^ Tourmaline is partially dissolved with re- 

 crystallization.^ In the Bolt district no trace of original minerals 

 has been detected even in the least altered of the schists. In the 

 diabases the amount of alteration is irregular. Near Dartmouth we 

 1 Plate 7, fig. 2. 2 pi^te 7, fig. 1. 3 Plate 6, fig. 2. 



