s. s. BUCKMAN, 
20 
(Schwed. Südpolar-Exp. 
is larger, and the description says that both valves are flattened along the middle, 
which could not possibly apply to the Antarctic fossils. 
There are 15 specimens of this species nearly of similar size, and having the 
appearance of being adult forms. Among them are some differences: some forms 
are narrower than others; some are strongly marked with growth halts, having the 
appearance of being aged shells; some show little of such halts. 
Besides these there are 4 small specimens, the two smallest of which have been 
figured. It was at first thought that these two small examples — one perfect about 
3,5 mm long, the other, broken, showing interior septum, about 2 mm long — might 
belong to the genus Cryptopora (Atretia, Neatretia)'^ but the septum which is shown 
PI. Ill, fig. 3 b, is placed more anteriorly and is directed differently from that of 
Cryptopora (see Atretia, Davidson, Recent Brach. PI. XXV), while it agrees with 
the septum which can be seen in the example of Magasella australis depicted in 
PI. I, fig. 16. 
Small examples of this species and of Hemithyris antarctica are very similar; 
and it is not easy, even with the microscope, to see the distinctive difference of the 
test structure. 
Locality: Cockburn Island (12), off Graham Land, Antarctica. 
Formation: Pecten Conglomerate. 
Material: Fifteen specimens nearly all in good condition; and four small 
examples. 
Note: The recent Magasella aleutica is found at depths of from low water to 
10 fathoms. 
Genus Pachymagas, Jhering. 
Type Terebratella tehuelcha, Jhering. 
1903. Jhering, Brach, tert.; Mus. Nac. Buenos Aires, (3) II 332. 
‘Comparée avec T. dorsata, le plateau cardinal [de Terebratella tehuelchci\ 
comme aussi ses annexes et le septum, sont extrêmement grossi et ses caractères 
servent pour établir un sous-genre, pour lequel je propose le nom de Pachymagas. 
' On the ground that Cryptopora was preoccupied by Crypioporus, and Atretia by Atretium, Fischer 
and Oehlert proposed and used the name Neatretia (p. 122). But though in the case of trivial names 
eryptoporiis and cryptopora would have to be regarded as synonyms, because the termination must be governed 
by that of the generic name, in the case of the generic name itself, there appears to be no necessity to 
make any change of termination; so that Cryptopora and Cryptoportis as generic terms ought to be quite 
distinct enough. It is true that such changes of generic termination were commonly made at one time; 
but such alterations are now discarded in favour of the original selection. 
