Bd. III: 7) ANTARCTIC FOSSIL BRACHIOPODA. 1 5 
A general description will cover the various Antarctic forms, and then their 
difterences can be indicated without undue repetition. 
The shape develops from subcircular to oval to elongately elliptical, these 
phases following one another in this order, with the usual tendency for the earlier 
stages to yield to the later at ever earlier periods of life (tachygenesis). Growth- 
lines are periodically conspicuous, forming growth-halts; and from these the various 
stages of morphogeny can be learnt. These growth-halts give the shells a banded 
appearance. 
In the dorsal valve, which is somewhat arched transversely and longitudinally, 
there may be a very slight sign of a median sulcus. Anteriorly this valve is slightly 
produced and reflected to fit into the notch formed by the more or less (longitudi- 
nally) carinate ventral valve, and there may be a slight anterior median depression. 
The beak area is large, less pronounced in the rounder, more pronounced and 
elongate in the narrower, forms. The hinge-line varies from nearly straight to 
rather sloping. The deltidial plates are large but not very distinct. The foramen 
is apical and subcircular. The test, where the outer layer is at all eroded, shows 
very hne punctuation. 
The following are the species and their characters: 
1. BoncJiardia ovalis: Broad form, not much carinate. 
2. Bouchardia antarctica: Elongate with straight sides (elongately elliptical in youth), 
strongly carinate. 
3. Bouchardia angusta: Elongately ovate, widest part at hinge-line, thence tapering; 
not strongly keeled. Hinge-line nearly straight. 
4. Bouchardia elliptical Elongately elliptical, with curved sides, broadest about 
middle; not strongly keeled. 
5. Bouchardia attenuata: Narrow elongate form, with little ventral carination; so 
dorsal growth-halts do not show anterior median angular projection, but are 
rounded. Hinge-line sloping from middle. 
The first three species differ considerably from the Recent B. rosea; especially 
is B. angusta distinct by its peculiar broad straight hinge-line. The other two 
species are like the Recent form, but neither tapers so quickly anteriorly or posteriorly, 
while in B. attenuata the whole shape in narrower, and in B. elliptica the beak is 
larger and less acuminate. 
The contours of the growth-halts show that in the young or youngest stages 
the species of Antarctic Bouchardiae are almost circular. This indicates that the 
earliest species of Bouchardia should be nearly circular in their adult stages: B. 
zitteli and B. patagonica almost conform to this state. In the Antarctic species 
the length is decidedly greater than the breadth in the broadest form; and in the 
narrowest form the length is nearly twice the breadth. 
