55 
half ofF, there is a tubular cavity (filled with rock) coming up obliquely from 
between the beaks and passing out anteriorly ; and this cavity was probably 
the byssiferous channel.”^ 
In neither of Prech’s figures is tins canal shown, but Waagen^ refers 
to it as a “narrow slit” in the right valve only, but the left valve [E. globosum, 
Waagen) does not appear to enter into the constitution of the byssiferous 
canal at all. Waagen says : — “ The byssal furrow of the right valve is thus 
left free by the other valve, which this gives room for the passage of the 
byssus.”® 
Freeh's Smooth Surfaee. — Dr. Freeh seems to be the only writer who 
regards the articulus of Eurijdesma as divisible into two main regions, the 
ligamental area proper, and a smooth, flat and broad surface below the latter; 
this character was used to separate his genus Leiomi^alma from Eurydesma 
(p. 45). Waagen in his description of the hinge structures of the Indian 
species referred to Eurydesma, did not refer to this smooth surface ; it is to 
he seen in Johnston’s figure of E. cordatum,^ and by Boehm is referred to as 
the “ hinge-plate — Avith which Ave are in agreement. 
(c) Cardinal Folds, “ Teeth " and Lnjlections. — The term cardinal 
fold is used for the so-called teeth in Eurydesma , which loosely fit into 
inflections of the hinge-plate, teeth and sockets in the true sense not being 
developed. 
Boehm remarks® : — “ One cannot appropriately consider as valve teeth 
the archings of the shell-vnargin, and are, therefore, distinctly visible from 
the outside.” . . . . “ the projection of the margin of the left valve 
simply extends over the margin of the right valve.” 
In E. cordatum it is found that in the right valve the cardinal fold 
rises as a blunt protuberance on the ventral margin of the hinge-plate, projects 
horizontally and is a continuation of the byssal ridge, whicb extends diagonally 
across the entire area from the umbo apex, and which bounds the byssal 
sinus posteriorly and separates it from the posterior portions of the hinge 
mechanism — Avlien the valves are in apposition this fold is invisible. 
’ Dana in AA'ilkes — Op. cit., p. 699. 
® AA^aagen — Op. cit., p. 137. 
* Waagen — Loc. cit., p. 140. 
^ .Johnston — Loc. cit., PI. XVII, fig. 2. 
* Freeh — Centralbl., loc. cit., p. 299. 
* Boehm — Loc. cit., p. 298. 
D 
