■m TAGE 8KU(iSDEI{<l 



aliiiost circular opening. The siphon is cut oft' anteriorly by a narrow, high, irregular wall, 

 diftering somewhat on the right and the left valve; communication between the siphon and the 

 larger anterior cavity of the shell takes place principally through a rather narrow, irregular 

 opening situated at about the centre of this separating wall (this opening marked by* in the 

 adjoining figure) and on the left valve by means of a smaller opening situated dorsally (shown 

 by** in the figure mentioned). For further details about the structure of this separating wall 

 it seems to me most convenient merely to refer to the accompanying fig. LII. Dorsally a short 

 distance in front of this wall, there is on both the right and on the left valve a rather long and 

 somewhat irregular peg, directed downwards and somewhat backwards. On the right valve 

 the hinge is furnished with a long, wing-shaped and rather strongly projecting tooth; this tooth 



. /* 



fig. Lll. — C. iSiphunostru) spinijcra n. sp. — The posterior p^irl ui tliu ^lit-ll seen from inside. 1. laylil valve, 5'. 



•2. Left valve, juv. <^. 



suddenly ceases anteriorly, a striking, almost rectangular, corner is formed, and decreases 

 gently and uniformly in height posteriori}'. ( )ii the left valve there is a cavity corre- 

 sponding to this tooth. (In the accompanying figure 5 this tooth is only indicated 

 schematically by a curved line.) I did not succeed in finding any hinge tooth posteriorly 

 either on the right or the left valve. The selvage is very wide along the anterior and 

 posterior margins of the rostrum and along the jjosterior margin of the rostral incisur — 

 the incisur is quite filled by it — and along the anterior part of the venti'al margin of 

 the shell; it continues along the whole ventral margin of the shell, extending somewhat 

 outside the edge. It is uniformly and finely cross-striated and is extremely finely, almost 

 invisibly, serrated at the edge or else smooth-edged. The shell is |)resuinal)ly rathei' 

 strongly calciferous — although the type specimen had a soft shell, not calcil'erous; a larva, 

 preserved in the same lii|Mi(l as the type specimen, li.id in its sliell nuinerous rounded 

 calcareous concretions, 



