ORTHIDtE. 261 



Sedgwick. It was also found by Mr. H. Wyatt-Edgell in the Caradoc at Troutbeck, but 

 there much out of shape from the effects of cleavage. The same geologist informed 

 me that he had foui^d specimens in the Lower Llandovery, but I know it only from 

 the Caradoc. 



Orthis ? HiRMANTENsis, M'Coy. PL XXXII, figs. 5 — 9. 



Orthis Hirmantensis, M'Coy. Annals and Mag. of Nat. Hist., 2nd ser., vol. viii, 

 p. 395, 1851 ; and Brit. Pal. Fossils, p. 219, pi. i H, fig. 1 1, 

 1852. 



— — Salter. Mem. Geol. Survey, vol. iii, p. 267, 1866. 



— — Id. Siluria, 4th ed., p. 526, 1867. 



Spec. Char. " Truncato-orbicular, depressed ; cardinal area very low, triangular, 

 nearly twelve times wider than high ; hinge-line slightly less than the width of the shell ; 

 cardinal angles slightly obtuse ; lateral and frontal margins horizontal, almost uniformly 

 curved ; entering [dorsal] valve perfectly flat, with a slight longitudinal mesial depression 

 near the beak; receiving [ventral] valve shghtly and gently convex, most so along the middle, 

 at about one third the length from the beak ; both valves with numerous shghtly unequal, 

 prominent, angular, strongly fasciculated strige, each of the primary ridges branching near the 

 middle into from five to seven smaller, forming in some specimens slightly angulated, 

 divaricatingly arched groups ; eight or ten strise at the cardinal angles, smaller and 

 straighter than the rest, running nearly parallel with the hinge-line ; separating sulci 

 narrow, marked with very coarse punctures or little pits, and crossed by coarse, obtuse, 

 transverse striae ; twelve to fourteen striae in two lines, at four lines from the beak ; 

 internal cast of receiving valve radiated with coarsely punctured impressions of the 

 external striae. Cardinal teeth very short, thick, diverging at 80°. 



'' Width 1 inch, proportional length ^^q, depth ^q." (M'Coy.) 



06s. I have not been fortunate in procuring satisfactory material with reference to 

 this shell, which, adds Prof. M'Coy, " is an extremely beautiful species, remarkable for 

 its flatness and broad divaricating bands of coarse, branched striae, which are not at all 

 arched along the hinge-line, as in the somewhat similar 0. retrorsistria (in which the 

 depth is greater, the striae much more uniform, and the surface smoother, and the 

 internal casts quite difierent).^' I have, therefore, deemed it preferable to reproduce 

 Prof. M'Coy's entire description, than to attempt an independent one of a shell I do not 

 quite understand. It was even suggested by the Rev. H. Day that a Strophoniena found 

 by him abundantly in Lower Silurian shales at Fary Gill, Cautley, near Sedberg (see our 

 PI. XLVII, figs. 1 — 4), might represent the complete condition of the so-termed Orthis 

 Hirmantensis, M'Coy. Under the uncertainty I feel concerning the generic and specific 

 claims of M'Coy's shell, I have preferred to describe them separately, and especially 



