86 . DEVONIAN FAUNA. 



Localities. — A single specimen from Top Orchard is in the Barnstaple 

 Athenaeum, its mould being in the Porter Collection. 



Bemarlcs. — Though this specimen is so imperfect that its full shape, &c., cannot 

 be ascertained, I have figured it, as it does not seem at all in accord with any of 

 our other fossils. Its extreme elongation and the uniformity of its contour is 

 remarkable, even if partially induced, as is indicated by a specimen of Orthis 

 interlineata, Sow., on the same slab being slightly distorted in the same direction. 

 The nearest approach to it is the shell recently described by Dr. Kayser, from 

 Belgium, under the name Phthonia, cf. cylindrica, Hall,^ which is so like that it may 

 perhaps prove identical. From Hall's own species the differences are greater. 



A fragmentary shell, from South Petherwyn, in the Museum of Practical Geology 

 has nearly the same dimensions, but differs so much in detail as evidently to be 

 distinct. 



III. i^a-rtuV?/— Prothyeid^, 8. A. Miller, 1889. 

 1. Genus — Prothyeis, Meeh, 1869. 



Shell equivalve, very inequilateral and transverse, moderately convex, con- 

 centrically striated, gaping and rectangularly notched in front, close or slightly 

 gaping behind ; umbo depressed, subterminal, with a small (elevated) fold running 

 from it to the anterior notch ; inferior margin direct, convex or re-curved. 



There seems one discrepancy between the genus as generally defined, and the 

 characters shown by English species, viz. that the notch in the latter is the termi- 

 nation of an elevated ridge running from the umbo, and not of a groove, as appears 

 indicated by Meek, Hall, Zittel, Fischer, &c. Whether this points to a real 

 difference I cannot say, but the character of the ridge in the English shells is clear. 



The species appear to be gregarious. 



1. Prothyeis recta, n. sp. Plate IX, figs. 12 — 14. 



Description. — Shell rather small, transverse, slightly convex. Umbo low, 

 incurved, situated at about the anterior third of the length, inclined forward. 

 Hinge-margin long (details unknown). Anterior margin broad, roundly convex, 

 with a small triangular notch or nick at its centre. Inferior margin long, very 

 slightly convex. Postero-inferior corner produced, narrow, very convex. 

 Posterior margin nearly straight, very oblique. Surface with unequal, low, 



^ 1885, Hall, ' Pal. N. T.,' vol. v. pt. 1, No. 2, p. 473, pi. Ixxviii, figs. 1—4. 



