President's Address. 19 



not be forgotten that Professor Geikie liacl already, in 1867, 

 expressed an opinion that some portions of the series might 

 with advantage be referred to the age of the Wenlock group.* 

 The number of shells determined by Messrs Brown and 

 Henderson from the fossiliferous Silurian strata of the Pent- 

 land Hills, may be taken in round numbers as — 



Brachiopoda, . . , 25 species. 



Bivalves, . . . 19 or 20 species. 



Gasteropoda, . . . 11 species. 



Pteropoda, ... -^ „ 



Cephalopoda, ... 7 „ 



Total, . G5 species. 



Of the Brachiopoda twenty species are decidedly of a Wen- 

 lock facies, whilst eighteen of these alone occur in the 

 Bed D. The Bivalves show a similar inclination towards 

 the Wenlock. Only six out of the nineteen or twenty species 

 are exclusively Ludlow, the remainder being again Wenlock. 

 Brown and Henderson added by their collecting much to our 

 knowledge of the Upper Silurian Brachiopoda, discovering 

 for the first time in Britain the peculiar Stropliomena Walm- 

 stedti (Lindst.). f The whole of their collections in this class 

 of Mollusca were examined and determined by Mr T. David- 

 son, and form the subject of a separate work, " The Silurian 

 Brachiopoda of the Pentland Hills," J and published about this 

 time. In this useful and highly scientific work are enumerated 

 no less than twenty-six species of Silurian Brachiopoda as 

 occurring in the Pentlands. Of these Lingida lata (Sby.), 

 Spirifera crispa (Linn.), Meristella Maclareni (Haswell), 

 and Rhynchonella Pentlandica (Haswell), all from Bed H, are 

 Ludlow species, and characteristic of that group, whilst the 

 remainder are decidedly Wenlock. One entirely new shell 

 is described, the Stro2)homena Hendersoni (Davidson), and 

 another rare form, not frequently met with in the British 

 Islands, the before-mentioned Strophomena Walmstedti. The 

 mineral condition of the Pentland Hill fossils is peculiar and 



* Trans. Geol. Soc, Glasgow, 1868, iii., pt. 1, p. 94. 



ilhid., p. 23. X 4to, Glasgow, p. 24, pi. 3, n. d. 



