382 Herman Friele 
nection with the seplum is broken of, and there remains but a 
little lump of the latter in the bottom of the valve. The wed- 
geformed separation of the lamellæ have progressed so far (Fig. 
7) that only a short band of connection is left between them; 
the apertures in the walls have likewise widened, and a narrow 
slip is all that still combines the lower and the upper parts. 
The stage of growth illustrated by Figs. 5—7 may.pro- 
perly be designated the Megerlia Stage, and it would be diffi- 
eult to recognize in this state either the individual deseribed in 
Figs. 1 and 2, or the fully developed Walheimia. In order to 
become a mature Waldheimia the band between the lamel-pro- 
cesses and the loop must vanish and the connected lamellæ 
must separate. 
The above mentioned «Bidrag til Vestlandets Mollusker« 
represents in Tab. 1 Fig. Å the very stage of development, 
when the tie between the upper and lower parts is broken, for 
remnants of the two vertical walls are still remaining on the 
lamel-processes, but as this specimen unfortunately has been 
lost, I am now unable to furnish a new and improved drawing 
of it. The skeleton at this stage begins to grow very fra- 
gile, and it is difficult to obtain good preparations. 
Fig. 8 represents a somewhat further advanced specimen; 
the hinder connection between the upper and lower parts is com- 
pletely severed, but the lamelle are still, though slightly, con- 
nected. Figs. 9 and 10 show this tie cut, and Fig. 11 an al- 
most mature Waldheimia cranium. The sizes of the latter 
stages are: Fig. 8—6,5 m. m. Fig. 9—6,6 mm, Fig. 
Fig. 10 —7 m. m. and Fig. 11— 8 m. m. (hoemale valves). 
My investigations of the Waldheimia septigera have not 
been made under semilar favorable circumstances as regards 
amount of material, but the accordance shown by both in their 
respestive development is so great, that one may well supply 
the place of the other in the filling up of any possible gap. 
Figs. 12 and 13 are W. septigera in the same stages as 
