PHOLADOMYA. 249 



Affinities. — By some autliors tliis species has been identified with P. Martini, 

 Forbes. With the matevial at present available it is difficnlt to make a satisfactory 

 comparison ; but the specimens from Speeton are of considerably larger size, with 

 broader and less prominent nmbones, and with the posterior part of the shell less 

 compressed than in P. Martini. 



In form tliis species resembles P. alternans, Roraer,' l)ut tlie nmbones are 

 relatively higher, and the radial ribs more numerous. The ribs arc not so numerous 

 as in P. Eherfi, Wollemann." 



EemarJi:s. — The specimens from the clays are considerably crushed, whilst in 

 those from the hard nodular beds a more or less considerable portion of the 

 marginal part of the shell is missing. 



Difiribntion. — Speeton Clay (zones of Bclenmites lateralli, B. jaculnni, and B. 

 bnmsvicensis) of Speeton. 



PuoLAUO.MYA M.vitTixi, Forbc-^, 18-t-j. Plate XLI, tig. o. 



18i5. Pholadomya MiRxiNi, E. F.jrhe.-!. Quart. Jourii. G-aol. Soc, vol. i, p. 233, 



pi. ii, fit;. 3. 

 18-50. — — A. d'Orhhpi;/. ProJr. (le Pal., vol. ii, p. 117. 



1854. — —J. Morris. Cat. Brit. Poss., ed. 2, p. 220. 



1865. — —F.J. Piclet and G. Campiche. Foss. Terr. Crct. Ste. 



Croix (Mater. Pal. Suisse, ser. 4), p. 92. 

 ? 1908. — — A. Wollemanii. Jahrb. d. k. preuss. geol. Laudes- 



anst. fiir 1908, vol. xsix, p. 165, 

 pi. X, fig. 3. 



Description. — Shell rather small, oval, very inequilateral, anterior part inflated, 

 posterior part compressed. Unibones prominent. Escutcheon, deep. Ornamenta- 

 tion consists of numerous radial riljs, which are more or loss tu))erculate, and ai-e 

 more widely separated anteriorly than on the median part ; on the anterior and 

 postero-dorsal parts ribs are indistinct or absent. Concentric ribs and growth-lines 

 are present. 



Remarks. — It is difficult to give a satisfactory description of this species, since 

 the specimens seen are few in uuiuber, imperfectly preserved, and usually crushed. 

 P. Martini appears to be closely allied to P. Fahrimi, d'Orbigny (see below). It 

 also resembles P. hispanica, Coquand."' 



1 Wollemaun, ' Die Biv. u. Gastrop. <1. dcutsch. ii. liolliimliscli. Neocoms' (1900), p. 134, pi. v, figs. 

 9, 10 ; pi. vi, tig. 3. Speeiineus with fewer ribs from the Spilsin- Saudstoue aud the Claxbv Ironstone 

 of Lincolnshire approach P. alteniaiii more nearly than do the specimens from Speeton. 



2 Il)i.l., p. 136. pi. vi, fig. 4. 



3 'Mou. Aptien de I'Espague' (1865), p. 92, pi. vii, figs. 5, 6. 



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