THE BRACHIOPODA OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 381 
same stages depicted by Frigtm in the ontogeny of the type species, M. cranium 
(FRIELE, 1877, pl. i. figs. 2-2), the only point of difference being in the possession of 
a less number of spinules on the septal pillar. 
The number of pores per square millimetre in this specimen ranges from 120 to 124. 
The scale-like structure of the shell-mosaic is very clear. 
The second specimen from the same deposit, though slightly damaged, is interest- 
ing as showing a very advanced terebratelliform (or pre-adult) stage (Pl. II. fig. 18). 
The dorsal valve of this example measures: length, 8°75 mm.; breadth, 8°5 mm., and 
shows the final development of the loop almost achieved. The descending branches are 
broad, and possess two internal triangular apophyses indicating the position occupied by 
the transverse (jugal) band attached to the septum in the terebratelliform stage ; also 
very prominent spinules at the recurvation. The stage of this specimen is almost 
equivalent to that of M. cranium figured by Friete (1877, pl. i. fig. 10) and 
BEECHER (1895, pl. u. fig. 1: 1901, pl. xxiv. fig. 1). 
The descending lamelle are supported at their origin by vertical, slightly converging, 
crural plates; no cardinal process is yet present. 
The median septum is only very slightly visible and takes its rise immediately below 
the apex of the valve, whence it runs a distance of half the length of the valve and 
then ceases midway between the transverse band and the point of recurvation of 
the loop. 
In none of the fully adult specimens of M. diamantina which I have examined is 
there any trace of the connecting bands on the descending branches, though the spinules 
at the recurvation are still apparent but much reduced. The median septum, which is 
only feebly developed, is also much reduced in length and confined to the umbonal 
region, where it supports the rather prominent cardinal process. On either side are two 
short parallel median septa supporting the convergent, but not united, crural plates. 
The ventral valve of the above specimen (length, 10 mm.) shows a large foramen 
with rudimentary deltidial plates, beneath the anterior angles of which are the two 
rather prominent teeth. 
On the exterior of both valves several conspicuous growth-halts are visible; the 
shell-punctze = 112 per square millimetre (middle of the ventral valve). 
Though the material at my disposal is so scanty, it does not seem improbable 
that, judging from the stages just described, the intermediate phases in the meta- 
morphosis of the loop will show considerable similarity to those described by FRIELE 
in MW. cranwum. 
The correct relationship of M. diamantina with the sub-family Dallinine, a group 
so characteristic of the northern hemisphere, is thus clearly established by the trans- 
formations undergone by the brachial support. 
This fact, which is, I believe, the first recorded instance of the ‘‘ Dallinoid” type of 
development in austral waters, is of great importance, as it has hitherto been considered 
that the two phyla, of common origin, of the section Terebratella, v.e. the sub-families 
