B. Etheridge, jun. — Netv Carhoniferous Mollusca. 301 



F. Valdwlms, Huxley and Etheridge, Cat. Fos. Mus. Pract. Geol. 1865, p. 110. 

 F. Sawerbii, Hiuxley and Etheridge. 'Cat. Fos. Mus. Pract. Geol. 1865, p. 109. 

 A'viculopecten Sowerbii, Armstrong and Young. Cat. Carb. Fos. W. Scot. Trans. 



Geol. Soc. Glasgow^ 1871, iii. app.. p. 47. 

 F. {Fseud-ai7nisium ?) Bathiis, Be Koninck. Eeeh. Anim. Fos. Carb. Bleiberg, 1873, 



;p. 94, pi. 3, %. 19. 



Sp. chars. — Shell ovato-elliptical, or suborbicular, slightly convex 

 in the median line, flattened towards the margin ; ears small, pointed, 

 depressed, triangular, subequal, conate, their apices elevated above 

 the level of the beaks, forming a re-entering angle, nearly at right 

 angles with the general periphery of the shell, both separated from 

 the body of the shell, with their outer edges convex ; umbones 

 simple, straight, and pointed ; muscular impression large, and situ- 

 ated near the beaks and posterior margin ; shell thin and delicate; 

 surface ornamented with numerous close, fine, concentric lines. 



Obs. — When the shell is removed, the inner lamina is seen to be 

 covered with a series of beautiful V-shaped or zigzag markings, very 

 acute about the convex centre of the shell, but becoming expanded 

 and opened out towards the margins. The true shell often has the 

 appearance of a thin, almost smooth or slightly wrinkled skin, with 

 here and there a few concentric lines of growth ; now and then, under 

 certain conditions of preservation, a number of fine lines may be 

 seen in the substance of the true shell, especially when held at an 

 oblique angle ; these are probably a more perfect condition of parts 

 of some of the V-shaped striae. 



P. Soiverbii undergoes a considerable amount of change in form, 

 according to the pressure to which the specimens have been sub- 

 jected. We frequently find two deep grooves extending from the 

 beaks, one on each side ; the lateral portion of the shell from these 

 grooves to the margins becomes much flattened, and in some cases 

 even concave, but notwithstanding this, still retaining on the surfaces 

 from which the shell has been removed the characteristic V-shaped 

 markings. Again, pressure appears to impart to it a certain in- 

 equilateral aspect, so much so in some cases as to lead one to doubt 

 the true specific identity of the specimen in question. 



The present species was originally described by McCoy from an 

 Irish specimen ; but it was not until the publication of his large 

 work on the " British Palseozoic Fossils " that the peculiar V-strise 

 were noticed. In this work the species was referred to Klein's 

 genus Amusium, from the re-entering angle formed by the ears of 

 the shell. Under the name of P. Vcddaicus, Kej^serling and De 

 Verneuil had in the mean time figured the lower part of P. Soioerbii, 

 showing the characteristic markings, from the Carboniferous series 

 of Eussia. It is also the P. Batlius of D'Orbigny. 



Prof, de Koninck has lately pointed out ^ that Mr. Meek has pro- 

 posed for similar pectiniferous shells the generic name of Entolium, 

 but that this corresponds in a great measure with the section or sub- 

 genus Pseud-amusium of Klein, in which the learned Professor 

 places P. Sowerbii. He further remarks that it has considerable 

 affinity with P. avicidatus, Swallow, 



^ Descr. Anim. Fos. Bleiberg, p. 95. 



