236 I)EVONIAN FOSSILS. 



of the older rocks in form, and the peculiar twig-like mode of 

 branching of the ribs on the middle of the shell, and the straighter 

 and finer ones of the sides, bixt is distinguished by the very much 

 greater number of the ridges. As in the case of that species the 

 distortion is usually such, that I can make no probable approxi- 

 mation to the proportional length. The coarseness of the ridging 

 separates the present species from the American Strophomena 

 nervosa and S. bifurcata (Hall) of the Chemung group. 



Common in the Devonian shale of Polruan, Cornwall ; in the 

 reddish Devonian schists of E. Looe ; schists of Fowey. 



{Col. University of Cambridge.) 



Strophomena gigas (M'Coy) . 



Sp, Char. Rotundato-trigonal ; hinge- line equal to the width of 

 the shell ; sides gently convex, converging to a narrow, much- 

 rounded front ; valves much flattened, slightly convex ; sur- 

 face radiated with very numerous fine, close, obtuse striae, 

 separated by narrower finely punctured impressed lines, every 

 fifth, seventh, or ninth of which seem larger than the rest 

 (about sixteen striae in two lines at an inch from the beak, 

 fifteen in the same space at the margin 3 inches from the 

 beak) ; cardinal area broad : internal casts of receiving valve in 

 adult specimens show the pair of muscular impressions, form- 

 ing a slightly bilobed or subtrigonal mass, about one-third 

 wider than long, and reaching rather more than one-third the 

 length of the shell, each side marked with six or seven very 

 coarse radiating ridges ; mesial septum very small. Average 

 length 3 inches 2 lines, proportional width -^^^ to ^gg, width 

 of cardinal area nearly 2 lines. 



This gigantic species in its elongate-elliptical or subtrigonal 

 form, arising from the narrow rounded front, precisely agrees 

 with Orthis subarachnuidea of MM. D^Archiac and De Verneuil 

 (Geol. Trans. 2 S. vol. vi. t. 36. f. 3), but diff'ers from it in the 

 larger striae at subregular intervals between the group of smaller, 

 as well as its great size. I have seen and made drawings of a 

 large number of specimens in the private collections of persons 

 at or near Looe, although there is only one indifi'erent specimen 

 in the University collection ; I am therefore better prepared to 

 decide on the characters of the species than I should otherwise 

 have been. 



Common in the Devonian shale of Looe, and of Polruan, Corn- 

 wall. 



{Col. University of Cambridge.) 



