42 Prof. W. King on Spirifer cuspidatus. 
ing some large specimens from the neighbourhood of Galway*, 
of which the outer layer is completely silicified, exhibiting, as 
a consequence, merely the mineral structure (siliceous pins 
enclosed in cylinders) characteristic of palliobranchiate shells 
in the metamorphosed condition; on the contrary, the inner 
and much thicker layer consists of a greenish substance, which, 
from effervescing on the application of acid, and being some- 
what harder than calcite, may be considered to be arragonite 
All the sections I have made of the latter layer display the 
fibres more or less clearly ; but none of them exhibit the per- 
forations at all well; and these structures are very often alto- 
gether absent. In their most obvious condition the perfora- 
tions, or, speaking more precisely, their vestiges, appear as 
dusky spots, or aggregations of granules, which have a trans- 
lucency more or less approaching that of the fibres: both kinds 
are ill-defined ; and the latter are occasionally larger than the 
former. The fibres agree with those of the Redesdale speci- 
mens in undulating and parting asunder where the traces of 
perforations make their appearance (see figure 7). In many 
cases little more than mere openings in the fibres are the only 
evidences of a perforated structure ; and often, as in the Redes- 
dale specimens, even such indications have been obliterated, 
the fibres running on without any strongly marked deviation 
from parallelism, 
The histology of Spiriferina laminosa, and the changes it has 
undergone, bear a strong resemblance to what have been pointed 
out in Spirifer cuspidatus, with this difference: the perfora- 
tions are much the smallest in the latter species, and the fibres 
are not separated by their intrusion. But had the perforations of 
Sp. cuspidatus been of the ordinary size, there can be no doubt 
the imperforate spaces, and specimens, would have exhibited 
indications of them in the occasional opening out of their 
fibres where they have been present. Mr. Meek has supplied 
me with a piece of evidence which explains, as is equally 
the case with similar evidences furnished by Nos. 1 & 2 speci- 
mens, the absence of such traces of a perforated structure on 
the view I have advanced. He informs me that “in some 
instances” [the expression shows how exceptional they are] 
* The Irish specimens, which are larger than those I have examined 
from Redesdale, have often two more obscure ribs on the terminal point 
of each wing: the latter do not appear to have been individuals of such 
free growth as those found in Ireland. 
+ Siliceous pins occasionally occur in the fibrous inner layer; but they 
break through the fibres without causing them to part asunder: the latter 
terminate abruptly against the former, as is the case with the enlarged 
perforations in Mr. Morton’s specimen of Sp. cuspidatus (see fig. 6). 
