20 Proceeclings of the Royal Physical Society. 



characteristic. Either internal casts or external impressions 

 are the state of the remains, a mollusc or any other fossil 

 with traces of the shell or integument remaining, being a 

 great rarity. Some of the shells are met with in considerable 

 numbers — thus Ehynchonella Pentlandica occurs in millions 

 in Bed H, and is an essentially Pentland form. In Bed D, 

 Leptoina transversalis is the most abundant Brachiopod, 

 whilst numerous other instances might be cited. Mr David- 

 son has also pointed out how much smaller in size the Pent- 

 land species are than is usually the case with Silurian 

 Brachiopoda. 



Since the publication of Davidson's work, Mr J. Henderson 

 has added * two further fossils to this admirable list, Discinct 

 striata and D. rugata. In 1874 Mr D. J. Brown announced 

 the discovery of fossiliferous blocks in the conglomerate of 

 the Habbie's Howe gorge, Logan Water, f These blocks 

 contain a goodly number of fossils, corals, shells, and traces 

 of trilobites. The determination of such remains has been 

 rendered difficult by the mineralisation they have undergone. 

 Further, it not unfrequently happens, that in splitting these 

 blocks, instead of exposing the outer surface of the shells, the 

 substance is itself split and fractured. No true appreciation 

 of the surface characters can be obtained, and identification 

 is rendered very difficult. I would indicate the fossiliferous 

 blocks in question as one of the most interesting directions 

 for future research in the Pentland Hills. 



The latest addition to the fauna now under consideration 

 comprised eight species of Mollusca, made in 1874 from the 

 collections of Messrs Brown and Henderson. J These com- 

 prise a bivalve shell apparently referable to a Lower Silurian 

 genus Aiiibonychia, and named A. Hendersoni, and if correctly 

 identified, a very interesting fact. Two species of the charac- 

 teristic Silurian genus Pterinea were likewise observed, and 

 one of Modiolopsis. Two species of Ctenodonta also occurred, 



* " On some Silurian Fossils found in the Pentland Hills" (Trans. Edinb. 

 Geol. Soc, 1874, ii., pp. 373-375). 



+ " On the Silurian Kocks of the South of Scotland" [Ihid., p. 320). 



t Etheridge, ''Notice of Additional Fossils from the Upper Silurian of the 

 Peutlaud Hills" {Ihid., pp. 309-313). 



