Bd. III: 7) 
ANTARCTIC FOSSIL BRACIIIOPODA. 
21 
L’espèce typique est T. tcJmelcha et il faut placer dans le même sous-genre T. gi- 
gantea Ortm. et venter IH. Toutes ces espèces sont éteintes et restreintes aux dé- 
pôts tertiaires de la Patagonie; toutes ont la coquille lisse, tandis que dans Tere- 
bratella s. str. le processus cardinal, les crura et le septum sont minces, plus ou 
moins lamellaires et la surface externe des valves est munie de large côtes 
rayonnantes.’ 
There are several specimens of a species, which, judging from external charac- 
ters, belongs to that series to which JllERING has given the name Pachymagas. 
Unfortunately the material is in poor condition, so that it is difficult to see the cor- 
rect shape of the species, and there are no loops to be obtained for most of the 
examples are ventral valves. 
Pachymagas antarcticus, sp. n. 
Plate II, figs 5 — 7. 
Description: Obovoid; dorsal valve flattened, medially depressed, anteriorly 
curved to form a shallow sinus; ventral valve arched with a wide, subdistinct, me- 
dian fold. Anterior margin curved to form a ventral fold; lateral margins nearly 
straight. Beak massive, without definite ridges; foramen large(?). 
This species has some resemblance to Tercbratella venter^ Jhering (III, 5), but 
is longer, not so gibbous, has, so far as the imperfect material shows, an almost 
flat instead of an inflated, dorsal valve, a beak not incurved and a large foramen. 
From Tcrebratella giganten, Ortmann (Pat. Exped., IV, PI. XIV, 2) it is lon- 
ger in proportion to breadth and has a more definite ventral fold; while the ventral 
valve is much more gibbous. 
The likeness to the recent JMagelhmiia venosa as figured by Davidson (Recent 
Brach., PI. VIII, fig. 2) is very noticeable: but the Antarctic fossil is not so broad, 
has more marked sulcus and fold for its size, and would not attain the dimension 
of that shell. 
The likeness of this species to those which Jhering has placed in Pachymagas 
makes it probable that the internal characters will be found to be on the terebra- 
telliform instead of the magellaniform pattern; and that it will be of the particular 
terebratelliform pattern which JliERiNG describes for Pachymagas. However the 
material does not allow of this supposition being proved. 
It may be remarked that as species of Magellania pass through a terebratelli- 
form stage in their ontogeny, pointing to a terebratelliform .stage of phylogeny, 
the names Magellania and Tercbratella do not indicate proper generic divisions 
but mark the stage of loop-development attained. It is therefore more than likely 
that certain Magellania; are really Terebratellce which have attained the magellani- 
