DIASTOPORA. 
129 
the outer layer of the zoaria of Discosparsa a geiTuinal layer. 
!M. Pergens apparently does not, as the character is not mentioned 
in his diagnosis of that genus. The layer is also well developed 
in some species of Retecava (the Reticulipora of Pergens), where 
its structure appears to he identical with that of ^ Jlesenteripora^' 
though again it is not noticed in ]\I. Pergens’ diagnosis. 
Hence H. Pergens appears to u-^e the term ‘lame germinale ’ in 
a more restricted sense than did d’Orbigny, although what difference 
there is between the structure of this layer in Riscosparsa, 
Berenicea, Reptomulthparsa, and ‘ 2Iesenteripora ’ does not appear. 
In Jliiltisparsa foliac^a, Orb., there are several parallel vertical 
laminae separating the successive zooecial layers. D’Orbigny’ s 
figure does not indicate any structural difference between these 
laminae ; but H. Pergens claims only the middle one as a ‘ lame 
germinale.’ 
Until some structural difference be demonstrated, or even 
rendered probable, between this middle layer of Multisparsa and 
Mesenteripora and the similar supporting or ‘ zoarial lamina ’ of 
other genera, it seems inadvisable to accept the ‘ germinal layer ’ 
as a feature of generic value. H. Pergens seems to have been 
uncertain as to its significance, for he only included ‘ Mesenteri- 
pora ’ in the Entalopboridae with some doubt. 
A strong argument against the validity of this ‘ germinal layer ’ 
is given by the specimen of Diastopora auricularis figured on p. 134, 
in which the zooecia open on both faces in one part of the zoarium ; 
which elsewhere divides into two laminaB with the zooecia on only 
one face of each. Where the zoarium is double there is a strong 
‘ germinal layer,’ as in Mesenteripora ; where the zoarium is single 
there is only the thin reverse layer of typical Diastopora. The 
‘ germinal layer ’ or zoarial lamina appears to be a basal, calcified 
layer, epithecal ^ rather than germinal in character. 
Further evidence against the ‘ germinal layer ’ is given by 
recent specimens of Diastoporidse in the Zoological Department of 
the British Museum. Some specimens of Diastopora repens (Hasw.) 
illustrate clearly the nature of the zoarial lamina. The zoarium 
> It might be better to speak of this layer as epizoarial than as epithecal ; but 
from its analogy with the corresponding structure in corals, the less correct but 
now established term may be retained. 
K 
