77 
observing that Mr. Davidson considers it liable to ready modification according 
to the conditions under which it developed, and also to assume a large number 
of variations. The facility of alteration does not allow one to decide whether 
the Carboniferous forms related to Devonian forms are specifically different, 
as some authors claim, or whether they constitute a persistent group dating 
from the time of the Middle Devonian. 
Ilorizou and Localities . — I have found only some badly preserved 
specimens of this species in a compact black limestone from Yarradong, 
associated with some number of Orthis interlineata, Sowerby. In England 
it is not uncommon in the Devonian limestone of lYoolliorough, Barton, and 
Lummaton near Torquay, and in Belgium in the Beceptacidites Neptmii 
shale from the neighbourhood of Chimay. 
Genm — ATE^YPA, Lalnian. 
1. Atrypa reticulauis, Linneeus. 
jinoniia reticularis, Linnaeus, 17G7, Syst. Nat., Ed XII. p. 113. 
jltrypa ,, T. Davidson, 1865, Mon. Brit. Dev. Bracb., p. 53, pi. 10, fig. 3 and 4.^ 
,, ,, J. Hall, 1867, Pal. N. York, IV, p. 106, pi. 51-53. 
It appears to me useless to delay long over the synonymy and 
characters of this form so well known to Palajontologists and so widespread 
through the different beds of the Devonian and the upper beds of the Silurian. 
I will confine myself to remarking that among tlie specimens that have 
been submitted to me, several bad tlie spires well jireserved and quite similar 
to tliose of European specimens. Others are provided with the marginal 
expansions, some of them having an expanse of a centimetre. I may add 
that two of the specimens have the principal cliaracters of Atrypa prisca, 
Schlotheim, considered by my learned friend, Mr. Davidson, with whom I 
agree, as being only a fairly constant variety of A. reticularis. 
Dimensions . — The Australian specimens are usually of medium size. 
I have not met with any that in this respect can be compared to the gigantic 
individuals that are not uncommon in the Eifel and in the Districts of 
Chimay and of Couviu. 
A complete synonymy of this species will be found in the works of Messrs. Davidson and Hall. 
