CARBONIFEROUS FOSSILS. 387 



thick and broad folds, six to eight on each side (six or seven 

 in our specimen) . They are not quite simple, except near the 

 hinge, but furnished with one or two ribs on the sides of the 

 principal ones. The folds are rather angular, and much 

 broader than the furrows between them, but the sinus is as 

 broad as the largest ribs, and has about seven " fine, not broad 

 ribs/'"* one of which is central and more conspicuous. 



The ventral valve, according to Von Buch, is only slightly 

 convex. 



The variety Saranae (fig. 11) differs in having no central rib 

 in the sinus, which is therefore angular and deep ; but it 

 shows the faint ridges both in the sinus and on the principal 

 ribs. These are rather more numerous (fully seven) and dis- 

 tinct up to the hinge area, where the shell is sharply incurved. 

 The ribs are rounder and not quite so angular as in the other 

 variety. 



LOCALITY. Depot Point ; also in red limestone, Exmouth 

 Island (Belcher), with the next. 



PRODUCTUS CORA (D'Orbigny). 

 Plate XXXVL, fig. 12. 



Our figure is an expanded and somewhat irregular specimen 

 of the under (dorsal) valve, or rather the impression of its 

 surface on the red limestone. The margin in this valve is 

 abruptly turned down after the shell has attained a couple of 

 inches in length, to fit the corresponding portion of the upper 

 valve. This indicates that the latter must have been highly 

 convex, and there are other smaller specimens of the upper 

 valve from the same locality, more regular in form and with the 

 beak prominent. The striation in both valves is characteristic, 

 the wavy strise being elevated threads, with furrows interven- 

 ing wider than the ribs themselves. The strise increase in 

 number continually by implantation, appearing to bifurcate 



* In his figure the supplementary ribs are a little stronger than in 

 our specimens. 



