57 
that of the Hamhurg Museum specimen — it is shown on the right valve/ 
although in the letterpress it is spoken of as a “ single, very strong hinge- 
tooth in each valve, as Avell as tlie suspicion of a posterior tooth.” 
Dr. AVaagen gave particular attention to the hinge structure ot 
Enrydesma. He remarks that the nu)st conspicuous part of the hinge in the 
right valve of E. gloho.mm is a strong and prominent hlunt tooth, just helow 
the apex, extending outwards in a nearly horizontal position ; it is solid, and 
more or less spoon-shaped. He also remarks that in the right valve the 
“ ‘ ligamental furrow’ is limited helow hy a ridge which is highest just helow 
the aj)ex, and hecomes here tooth-like. It extends not v('ry far backwards, 
but disappears after a short distance.”’ According to Waagen, this fits into 
a deej) hackwardly bifurcating furrow just helow the umbo of the left valve, 
“ the lower somewhat more sloping part serves for the reception of the ridge- 
like sloping cardinal tooth of the other valve.” ^ 
Freeh’s statement that a tooth is ])res(mt in the left valve is not 
supported hy any other author ; in fact, Boehm denies the existence* * of such 
a dental development.^ 
Dana refers to a “ depression somewhat anteriorly [left valve] 
answering to a large rounded prominence or tooth in the other valve [right], 
as described hy Morris.”^ This is clearly the socket for the reception of the 
large dental prominence of the right valve, d’his depression or socket is 
shown in the right-hand lower figure of E. cordatnm, in i\[orris’ Plate XTI. 
Stoliezka speaks of it as a “ pit.”" 
In Freeh’s figure of the Hamburg sj)ecimen, the socket is represented 
simply as an infiection of the margin of the hinge-plate." 
It will he remembered that in Waagen’s d('scri])tion of the right valve- 
hinge apparatus of his E. glohosum, is mentioned a ridge-like, sloping cardinal 
tooth ; the socket for the reception of the latter is the lower portion of the 
suhapical bifurcating groove described hy him as occurring in the left valve.* 
* Freeh — Leth. Pal., loc. cil., p. 600, a np. fig. 
Waagen — Loc. cil., p. 139. 
’ Waagen — Loc. cit., p 140. 
* Boehm — Centralhlatt, loc. cil. , p. 298. 
* Dana in Wilkes — Loc. cil., p. 699. 
® Stoliezka — Op. cil., p. 226. 
1 Freeh — Leth. Pal., loc. cil., p. 600, a, lower fisr. 
* Waagen — Loc. cil., p. 140. 
