MY0PH0LA8. 253 



Pholadomya corpata, Tat<', 18G5. Plate XLII, fig. 2 <i — r. 



1865. PHOLADOMy.\ coEDATA, if. Tctte. Quart. Jmirn. Geol. Soc, vol. xxi, p. 4(), 



}il. iv, fii^. 1. 



BeniarliS. — A specimen fouml in the I'pper Chalk (zone of Jielemnitella mncro- 

 ■nata), now in the Norwich Museum (No. 3339), is probal)ly an example of P. 

 cordata, Ijut unfortunately the anterior part of the shell is imperfect. In this 

 species tlie anterior curvatni-e of the umbones is greater and the de2)ression in 

 front of them deeper than in P. decu.ssata ; also the anterior flattened part is 

 relatively smaller, since the greatest diameter of the shell occurs at about one third 

 of the lengtli from the anterior end. The ty})es of P. cardata from the Upper 

 Chalk of Ireland are in the Museum of Practical Geology (Nos. 23,(328 ; 28,629). 



Genus — Myopholas, H. BourilU, 1007. 



(' Bull. Soc. gcol. de France,' ser. 4, vol. vii. p. Iu7.) 



Myopholas, sp. cf. SEMicosTATA {Aijunsi::), 184-2. Plate XLIT, fig. 3//,/;. 



Descriptiun. — Shell oval, short, con.siderably ine([uilateral, anterior part convex, 

 230Sterior part compressed; anterior and posterior margins rounded. Umbones 

 curved inwards and forwards. Eather more than half of tlie shell — the anterioi^ 

 part — is ornamented with thirteen narrow, sharp, radial ribs, which are separated 

 by broad, flat, or slightly concave interspaces ; posterioi-h* these ribs become 

 smaller and less widely separated ; on the middle part of the shell a few indistinct 

 concentric ribs are seen. The posterior part of the shell is nearly smooth, and is 

 separated from tlie ribbed area l)y a slight depression ; a cui'ved carina extends 

 from the posterior side of tlie iiml)i) towards the postero-vciilral extremity. 



Affinities. — Only one specimen lias Ijeen seen; it resend)les closely M. seiui- 

 costata (Agassiz^), but is rather shorter, and the posterior limit of the ribbed area 

 is more sharply defined than in most examples of M. yciiiicoslnfa. Judging from 



1 'Etudes crit. Moll. Foss.,' Mves (1842), p. 51, pi. ii, figs. 1, 2, pi. iii', fig. 11. Pictet ami 

 Campiche, 'Foss. Terr. Crct. Ste. Croix' (' Mati'r. Pal. Suisse,' ser. 4, 1865), p. 77. pi. cv, figs. 1, 2. 

 Moescli, 'Mod. Phohulomveu ' (1874), p. 85, pi. xxx, fig. 4, i)l. xxxiii, figs. 3, 4. pi. xxxvi, fig. 1. 

 Douvillr, ■ Bull. Soc. geol. de France,' ser. 4, vol. vii (1907), p. 112, pi. ii, fig. 8. Jloescli includes as 

 a svnonvm PhoJadomya Trihohti, Pictet ami Caiiipiclie, op. cit., p. 8!l, \>\. cvi, fig. 8. Pictet and 

 CanipicLe include P. Moreuna, Buviguier, ' Statist, gi'ol., etc., de la Meuse ' (1852). Atlas, p. 8. pi. viii, 

 figs. 21. 22. 



