STROPHOMENIDJE. 309 



gently convex or almost flat. Surface of valves ornamented with numerous thread-like 

 radii, the ends of which project beyond the margin ;_ one or two smaller radii likewise 

 partly occupy the wide interspace left between each pair ; and the entire surface of 

 both valves is closely crossed by delicate ridges of growth. Interior not known. 

 Length 7, width 1 5 lines ; but usually much smaller. 



Obs. This shell was described for the first time in 1846. It is both smaller and 

 flatter than Str.peden, a closely allied species. Mr. Salter observes that the ribs project 

 like those of Venericardia, and produce a pectinated margin ; and that the small size of 

 the shell appears constant. 



I have examined many specimens of this small species from the Pentland Hills, 

 where it is associated with individuals of Stropli. pecten of all ages, and can always be 

 distinguished by its pectinated margin. 



Position and Locality. In ' Siluria ' it is stated to occur in the Llandovery and 

 Wenlock formations. I am acquainted with the shell from the last-named strata only. 

 In England it is mentioned by Phillips and Salter as being found at Craig-y-Garcyd, 

 Usk. 



In Scotland it abounds in Wenlock Shales in certain spots along the banks of the 

 North Esk in the Pentland Hills, and not far from the reservoir bearing that name. It 

 was discovered for the first time in Scotland by Mr. A. Geikie : but althoudi I searched 

 the locality for several hours, in company with Messrs. Haswell and Brown of the 

 Geological Society of Edinburgh, no specimen with the shell itself was ever discovered. 



In Ireland it is stated by Mr. Salter to be abundant in slabs at Cooling, Cong, in 

 company with OrtJns, or rather Strophomena corrucjata, Portlock. This statement will, 

 however, require confirmation, for the last-named shell is a Caradoc species, and I question 

 whether St. applanata has been found so low down in the series. 



Strophomena ornatella, Salter, MS. PI. XLIII, figs. 16 — 20. 



Strophomena ornatella, Salter and Lindstrom. Nomina Foss. Sil. Gotlandise, p. 5, 



1867. 



Spec. Char. Semicircular, wider than long, very slightly concavo-convex, much 

 depressed ; greatest breadth at the hinge-line ; cardinal extremities pointed, forming 

 small mucronate wings. Ventral valve very slightly convex ; area narrow, fissure arched 

 over by a pseudo-deltidium ; beak not projecting. Dorsal valve almost flat, or very 

 slightly concave ; hinge-area linear. Smface of both valves beautifully marked with 

 numerous thread-like ribs, radiating from the beaks to the margin, and leaving very 

 wide interspaces between them, which are occupied by two or three smaller ribs, 



