14 Proceedings of the Eoyal Physical Society. 



by these Durness beds to certain of the Lower Silurian rocks 

 of America. 



Murchison's paper detailing these facts, with Salter's 

 descriptions of the fossils, appeared in 1859.* We see at a 

 glance that the fauna discovered by Mr Peach consists 

 exclusively of two groups of shells only — the univalves and 

 chambered shells. Of the former the most important is, of 

 course, the large Machirea Peachii, a very remarkable species 

 of this strange genus. It possesses a massive operculum, 

 with a produced and spirally inrolled nucleus resembling a 

 Capulus, at once distinguishing it from its fellow species. 



The resemblance of Machirect to some bivalves of the group 

 Eudista has been commented on by several writers. It was 

 so referred originally by one of our first Conchologists, the 

 late Dr Samuel P. "Woodward,-f* and placed near the genera 

 CaiJTotina and Caprinella. Later Dr Woodward showed its 

 relation to the Heteropoda, probably a solid sedentary form 

 allied to Bellerophon.X 



A second species of Maclurea is also present, and appears 

 to be identical with an American fossil. 



The full list of Gasteropoda from the Durness limestone is 

 as follows : 



Maclurea Peachiiy Salter. 



„ matiUina, Hall ? (Calciferous Group of North 



America = Lowest Silurian) . 

 Hormotoma gracilis, Hall ? (Trenton and Hudson 



River Groups =Llandeilo and Caradoc). 

 Miirchisonia angulocincta, Salter. 



„ hellicincta, Hall ? (Ditto). 



Ophileta com])acta, Salter (Calciferous Group of North 



America = Lowest Silurian). 

 PUiirotomaria Thule, Salter (allied to P. siibconica, Hall, 



of the Trenton and Hudson E, Groups). 

 Rajohistoma lahrata, Emmons (Calciferous Group of 

 ISTorth America). 



* "On the Succession of the Older Rocks in the northernmost Counties of 

 Scotland," etc. (Quart, Jour. Geol. Soc, xv., pp. 353, 421); and ''Fossils of 

 the Durness Limestone" {Ibid., pp. 374-381). 



t Salter, loc. cit. % Man. MoUusca, 1851-56, p. 202. 



