﻿1851.] MURCHISON SILURIAN ROCKS OF SCOTLAND. 173 



Orthoceras vaginatum, Schloth. ? Pl. X. fig. 7. Of this we have 



but one specimen. 



■ . A small species, with waved transverse lines. 



Cyrtoceras , sp. Such are found both in Upper and Lower 



Silurian. Pl. X. fig. 8. 



Ardwell. 



Diplograpsus bullatus, Salter (comp. Graptolithus pristis of Hall). 



Pl. X. fig. 2. *** 

 Cyrtoceras. Same species as at Piedmont. 



Orthoceras angulation, Hisinger. Our specimen has coarser and 

 more distant ribs than usual. 



Orthoceras calamiteum, Miinst. and Portlock. The distinct longi- 

 tudinal ribs are not crossed by transverse ridges, but only by lines 

 of growth, as in some Irish specimens of this variable species. 

 This is Orthoc. annellatum, Hall, of M 'Coy's list, cited above, and 

 O. bilineatum, Hall (M'Coy in lit.). 



Prof. M'Coy' s list contains also Leptcena sericea and some other 

 fossils. And both at Ardwell and Glenquapple he finds Or this sim- 

 plex, M'Coy, and at the latter locality Leptcena sericea : — both are 

 Lower Silurian. 



Knockgeirn. 



Orbicula 1 crassa, Hall. A thin, finely striated shell, like O. stri- 

 ata, Sow. See description, p. 175. Pl. X. figs. 3, 4, and wood- 

 cut, p. 151. The same species occurs also in the Utica slate of 

 New York. 



Orthoceras politum, M'Coy. As above. Pl. X. figs. 5, 6. 



Descriptions of a few of the above Fossils. 



Graptolithus tenuis, Portlock, Geol. Rep. Londonderry, p. 319, 



pl. 19. f. 7. Pl. X. fig. 1. 

 G. tenuis, M'Cov, Synops. Classif. Brit. Palseoz. Rocks, Pt. 2. 



pl. 1 b. f. 4. 



Congregated stems of this slender Graptolite occur in Piedmont 

 Glen, which after careful examination I would refer to Portlock's 

 G. tenuis ; the original specimen of that species, however, is so ob- 

 scure as to afford no definite characters. Our specimens, 4 or 5 

 inches long, have not suffered sufficient compression to flatten out 

 all their parts ; the empty canal has collapsed, and the very oblique 

 cells show also a depression along their length from this cause ; the 

 narrow cell-mouths are very remote, each being opposite the base of 

 the cell above it. There is an indentation, slight but still very con- 

 stant, of the main canal opposite the base of each cell : Prof. McCoy's 

 figure does not show this, but he tells me that his specimens are 

 frequently so, and believes it to be the consequence of contraction 

 after death. 



Locality. Piedmont Glen. 



