The Development of the Skeleton in the Genus Waldheimia. 383 
illustrated by Figs. 3 and 4 of W. cranium. The only 
essential differences are in the form of the septum and the size, the 
latter being 4,5 m. m. and 5,5 m. m. respectively. The next stage, 
the Megerlia stage, is illustrated by Figs. 14 and 15. In Wald- 
“ heimia cranium the lateral walls were broken down by an aper- 
ture appearing in the middle of each and widening backwards; 
in Waldheimia septigera the breach oceurs to the contrary on 
the posterior end of the walls and extends in a forward direc- 
tion. At this stage the semilarity to Terebratella is striking, 
and a drawing of two specimens of T. spitzbergensis Dav., ob- 
tained on the Norw. North-Atlantic-Expedition in 1876, is in 
Pl. 6, Fig. 1 and 2 appended for the sake of comparison. 
Fig. 16 shows the connection between the lamel-processes 
and the septum severed, and in Fig. 17 the lamellæ are sepa- 
rated. 
The history of the development of the Brachiopoda has 
untill recently been very little known, and it was not till in 
1871 and 1873 that Prof. Morse published a complete deserip- 
tion of that of Terebratulina septentrionalis Couth. («Early 
stages of Terebrtl. septentrionalis« and «Embryology of Tere- 
bratulina’). By comparing the manner in which the formation 
of the apophysary system takes place in the latter with the 
above described in the Waldheimia, an essential difference is 
observed: Terebratulina proceeds without deviation direct to- 
ward the form that characterises the genus, Waldheimia to the 
contrary forms first a very complicated loop-complex, and passes 
then to the more simple construction. 
These two ways of development must surely also become 
the basis for two larger sections within the family of the Tere- 
bratulide, The living forms have been devided by Mr. W. H. 
Dall into the following subfamilies: Terebratuline, Magasine, 
Kraussinine, Platidiine and Megathyrine. The development 
1) Memo. of the Boston Society of Nat. Hist. Vol. IT, Part 1 and 3. 
26* 
