The development of the Skeleton in the Genus Waldheimia. 385 
resulted satisfactorily, mainly for the reason that I have had 
none but dried specimens to study. Pl. 3 Figs. 1—4 illustrate 
a series of such young W. cranium of the following sizes: Fig. 1 
L. 0,36 L. 0,60 
B. 0,26 B. 0,43 
Fig. 4. L. 2,8 m. m. — Figs. 5 and 6 are W. septigera, Fig. 
mms Wiese 2 nn bio need mem. 
5. I m. m., Fig. 6. 2,5 m. m. long. From this is will be seen 
that these two species already at an early stage deviate from 
each other in the shape of the margin of the hinge, which is 
truncate in W. cranium and pointed in W. septigera. Dr. Jef- 
freys. in Br. Conch. Vol. IT pg. 14 has called attention to the 
fact that the young of W. cranium «have slight ears, or trian- 
gular expansions at the uppes angles of the lower valve». The 
foramen in W. septigera is complete in the young. At the 
stage represented by Fig. 4 the skeleton of W. cranium has 
not yet become coherent, the crura-processes only being devel- 
oped, and a septum may be seen in the form of a lump in the 
bottom of the valve. The occurrence of a septum at this early 
stage has also been mentioned by Dr. Jeffreys in Br. Conch. 
Vol. Il pg. 14. In W. septigera the apophysis in Fig. 6 sho- 
wed itself at the same stage as in Fig. 4. The septum is here 
a short sharpe ridge. 
Dr. Jeffreys has had the great kindness to send me his 
type-specimens of Gwynia (Argiope) capsula Jeff. for compari- 
son. My first glance at them sufficed to convince me that there 
can be no question as to their being «the fry« of W. cranium, 
for not only are both valves of very nearly the same size, but 
the form, the foramen and the structure of the shell are essen- 
tially different. The two diagrams Pl. 3 Figs. 7 a and b re- 
present side-views of both forms. Fig. 7 a W. cranium and 
Fig. 7 b G. capsula. The following measures of three speci- 
mens of G. capsula will suffice to show its great difference of 
L. 0,60 
the form from that of W. cranium: 1. B. 0,54 
m. Im... 
