;wii' r\iii; sk(I(;si!i:i!h 



almost riiTular oju'iiiii^. 'I'lif siphon is vu\ oil anteriorly hy a narrow, liigli. irrci;nlar wall, 

 tlifTiTinj; somewhat on tlif riuiit and tin' Iftl \al\i'; cdninuinical ion l)ci\\tcn tlic siplion and llu- 

 larger anterior cavity of tiie shell takes place princijiallx thiou^li a rather narrow, irregular 

 openinj,' situated at about the centre of this sej)aratin;; wall (this opening marked by* in the 

 ailjoining ligure) and on the left \al\i' ii\ means of a smaller opening situated dorsally (shown 

 by** in the figure mentioneil). For turt her details about the structure of this separating wall 

 it seems to me most convenient merely to refer to the ae(dni|)aiiying fig. Ul. 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. < >n the right valve 

 the lunge is furnished with a long, wing-shajied anil rather stroIlgl^■ projecting tooth; this tooth 





y 



^ A 



/ 



Kig, Lll. — C.ySiphonostra) spinifera ii. s|i. — Tlie posterior jiail ol Ihu slu'll srvn lioiii iii>-iili . |. lijulii, val\i. ■,. 



2. Left valvi'. jiiv. q. 



suddeuly ceases anteriorly, a striking, almost rectangular, corner is iornied, and decreases 

 gently and uniformly in height posteriorly. On 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 posteriorlv 

 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 posterior margin of the rostral incisur — 

 the incisur is quite filled by it — and along the anterior part of the ventral margin ol 

 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 presumably rather 

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

 preserved in the same liquid as the type specimen, had in its shell numerous rounded 

 calcareous concretions. 



