52 
reaches with its upper teriniiiatioii to near the apex.”^ In E. ellipticuyn, 
Waagen, tlie lunule is not “ very distinctly developed,” and in E. cordatum, 
Waagen, it is represented hy a “ shallow eniargination,” and “ not very 
excavated.”^ 
7. Articnlus, or Hinge Region. — This essential part of the shell may 
he considered under four suh-heads : — {a) hinge-plate, (Z») the resilifer, (c) 
hyssal sinus, [d) the cardinal folds (the so-called teeth), and the inflections 
re})resenting the sockets. 
W e are led to regard the whole of these structures as integral portions 
of the respective “ hinge-})lates,” and fail to appreciate the importance 
assigned by Dr. Drech to an upper and lower plate as distinctive of his genus 
Leiomyalma (see j). 44). In this connection Professor Boehm says : — “ I, at 
least, was unable to observe a decided fiat surface either in the figures or in 
the originals at Hamburg.”^ Furthermore, we do not admit the presence of 
“ teeth,” in the strict sense of the word, in the articulus of Empdesma^ and 
a ligament is absent. Our conception of the hinge region of Eurydesma 
dilfers widely from that of Dr. Waagen. 
In Morris’ figures the actual hinge-margiu appears to be convexly 
curved on the anterior side, and slightly sigmoidal on the posterior.* * Dana 
did not figure a complete hinge. Freeh, in his second illustration of 
Leiomyedina antarctica^ shows a generally semicircular outline, convex on 
either side of the umbo, the posterior element forming a wide, downwardly- 
sweeping curve. In the earlier figure of an articulus® the outline is much 
less convex on the posterior side. All Waagen’s figures of cardinal margins 
are sharply convex on both sides of the iimbo.^ 
(a) Hinge-plate. — Taken as a ivhole, each hinge-plate is triangular, 
but unequal sided, massive in comparison to the heavy, thick umbonal 
regions ; in E. cordatimi it appears to be larger and heavier in proportion in 
the left than in the right valve. 
‘ Waagen — Loc. cit., p. 140. 
" W^aagen — Loc. cit., p. 143. 
^ Boehm — Loc. cit., p. 299. 
* Strzelecki — Op. cit., PI. XII. 
® Freeh — Leth. Pal.., loc. cit., p. COO, fig. a. 
Freeh — Abhandl. Geol. Specialkarte Preuss. Thiiring Staateii, loc. cit., p. 203, fig. 22. 
’’ Waagen — Salt Range Fossils, loc. cit., Pis. VI-VIII. 
