Dr. H. Woodward — On Fossil Shells from Sumatra. 389 



the smallest. Size of largest valve : Long. 55 mm. ; Lat. 40 mm. 

 Size of smallest valve : Long. 30 mm. ; Lat. 22 mm. 



Locality and Formation: — From the Miocene Clay-marls, Island of 

 Nias, Government of the West Coast of Sumatra. 



10. Lucina, sp. (cast). PI. X. Fig. 7. 



This is evidently a cast of Lucina, but the state of preservation 

 precludes the possibility of offering an opinion as to the species to 

 which it should probably be referred. 



Locality and Formation: — This cast was obtained from Government 

 of the West Coast of Sumatra, "Stage 5" of M. Yerbeek, Coral- 

 limestone "including internal casts of Gasteropods and Conchifers, 

 together with Echinidce comparable with the Eocene forms Prenaster 

 Alpinus, Desor, and Periaster sub-globosus, Desor." (Verbeek, Geol. 

 Mag. 1877, p. 444.) 



Gen. Isocardia, Lamarck, 1799. 



Shell cordate, ventricose ; umbones distant, sub-spiral ; ligament 

 external; hinge-teeth 2 : 2 ; laterals. 1-1 in each valve, the anterior 

 sometimes obsolete. Of this genus five species are recorded from 

 Britain, Mediterranean, China, and Japan, and 70 fossil species 

 from the Trias and higher formations. 



H. and A. Adams, in their Genera of Eecent Mollusca, 1858, vol. ii. 

 p. 461, have proposed, for certain forms of Isocardia, a subgenus. 



Sub-genus Meiocardia, H. and A. Adams, 1858. 



" Shell with the surface of the valves concentrically grooved, not 

 covered with an epidermis." (Valves strongly carinated at the posterior 

 end, forming a prominent acute diagonal ridge. Posterior slope con- 

 cave.) To this subgenus has been referred : — M. Lamarckii, Sby. ; M. 

 Molikiana, Chem. ; M. Cumingii, A. Ad. ; M. tetragona, Adams and 

 Reeve : M. vulgaris, Eeeve ; all recent forms : also M. Guerangeri, 1 

 d'Orb. (Cenomanien), Chloritic marl of Le Mans ; and M. (Isocardia) 

 pyrenaica, d'Orb., from the Cretaceous of Corbieres, Aude, France. 

 This latter form, however, we should be more inclined to refer to 

 the genus Opis. 



11. Meiocardia sub-Cumingii. PI. X. Fig. 10. 



Of the various species of Meiocardia, it is very interesting to 

 observe that the recent M. Cumingii from China seems almost 

 identical with our fossil ; the only perceptible variation being that 

 in the recent form the raised concentric ridges are about 24 in 

 number, whereas in the fossil there are upwards of 30. In the 

 fossil form the diagonal ridge is even more prominent and acute 

 than in the recent species, and the posterior slope more concave. 

 These are the only points deserving of special attention — save that 

 one of the fossils (casts) is much larger than the recent form ; 

 probably half as large again as the specimens of M. Cumingii from 

 China in the British Museum. 



1 Not mentioned in the text of d'Orbigny; but marked on his plate 257bis. as 

 "Isocardia Guerangeri, d'Orb." In his Prodrome de Paleontologie Stratigraphique 

 Universelle, vol. ii. 20 Etage Cenomanien, jSTo. 290, p. 160, however, he enters it 

 as " Opis Guerangeri, d'Orb, 1843." 



