50 
forward.^ Stoliczka, reviewing Morris’ and Dana’s works, regarded them as 
strongly incurved.^ Waagen, in writing of E. globosum, M"aagen says: — 
“We find that this latter [apex or umbo] is very narrowly rounded, very 
strongly prominent, and not very much bent over.”^ In E. ellipticum, 
M^aagen, “ the apex of both valves is tolerably broadly rounded ” ; and in 
E. cordatmn, W'aagen, the iimbones are nearly median, “ the apex is tolerably 
prominent, but not distinctly marked off from the remainder of the shell,” 
but well bent over and pointed. 
5. Inequality of Valves. — Dana described the shell of Eurydesma as 
inequivalve, figuring the valves of E. elliptica in support.^ In his figure 
it will he seen that the umbo of the left valve is at a lower level than that of 
the right. From an examination of a large series, it is found that this is a 
very variable character. It is certainly present in some specimens of E. 
cordatum to a slight extent ; it is just as certainly absent in others — on the 
other hand, the hinge-plate of the left valve always appears to be a more y. 
massive structure than that of the right valve, as will be seen later (p. 52), 
notwithstanding that the articulus of the right valve is a more comjilex 
structure than that of the left. Mbaagen considered the right valve to be 
the larger,^ and drew particular attention to E. elUpticwn, Waagen.® As a 
general rule the valves in our specimens are eqvial when viewed externally. 
IMorris described the shell as equivalve, Dana as inequivalve. This inequality 
is very clearly shown in two of his figures of E. elliptica,^ where the left valve 
not only has a smaller and lower umbo, but is also decidedly less convex. 
The flanks are, as a rule, evenly rounded from apex to ventral margin, 
hut certain specimens figured by Dana show variations. In E. elliptica, 
Dana,® the regular contours are directed inwards on approaching the ventral 
margins and then again bent slightly outwards, the profile l)eing slightly 
sigmoidal — this is more apparent in the left fhan in the riglit valve. In 
Dana’s E. sacculus the ventral inflections already referred to end above in 
ill-defined longitudinal cinctures, almost extending for half the height of 
the valves. 
* Dana in Wilkes — Op. cit., p. 699. 
’ Stoliczka— Cret. Fauna, loc. cit., p. 226. 
’ Waagen — Salt Range Fossils, loc. cit., j). 138. 
* Dana in Wilkes — Op. cit., p. 699, PI. VII., fig. 6c. 
’ Waagen — Salt Range Fossils, loc. cit., j). 138. 
' Waagen — Ihid., p. 141. 
’ Dana in Wilkes — Op. cit., I’l. VII., figs. 6/^ and c. 
* Dana in Wilkes — Op. cit., PI. VII. figs. 6ft and c. 
