Spirifer cuspidatus and of certain allied Spiriferide. 71 
inch from each other. They are not distributed, however, with 
the uniformity which usually prevails in the shells of the per- 
forated Brachiopoda ; for patches of imperforate shell intervene 
between portions that are pretty regularly perforated, and some- 
times a fragment large enough to fill a great part of the field of 
view is entirely imperforate. This, I feel certain, is not the 
result of any alteration produced by fossilization, the shell- 
structure being equally well preserved in the perforated and in 
the imperforate parts. Prof. Winchell speaks of this shell as 
“jmpunctate in all conditions and under high powers,”’—a 
statement for which I can only account on the supposition that 
he happened to examine only minute fragments which chanced 
to be imperforate, as occurred to myself in my first examination 
of No. 4. 
2. The Spirifer cuspidatus and Sp.subcuspidatus of the United 
States paleontologists are unquestionably perforated ; and pre- 
cisely resemble the preceding not only in the size of the per- 
forations and in their distance from each other, but also in the 
patchiness of their distribution. 
8. The Millecent (Irish) shell in Mr. Worthen’s possession 
exhibits exactly the same combination of imperforate with per- 
forated structure ; and I have no doubt that it was the uncer- 
tainty produced by this peculiarity which led Mr. Meek, in 
transmitting me chips for examination, to express a doubt 
whether he had been originally correct in asserting the presence 
of perforations in this shell. 
4. The two Millecent specimens obtained for me by Mr. Jukes 
also unquestionably exhibit the same character of patchy per- 
foration; but I might not have ascertained the existence of 
perforations if I had not carefully scrutinized every lamella of 
shell that I could scale off, all the fragments first examined 
having chanced to be imperforate. 
5. Mr. Davidson’s typical specimen of Spirifer cuspidatus, 
also from Millecent, exhibits not the smallest trace of perforations, 
though I have scaled off from it flakes of such size, and from so 
many different parts (including also both its outer and its inner 
layers), that I feel justified in confidently asserting that this 
- shell is essentially zmperforate. 
Thus, then, whilst my previous determination of the imper- 
forate structure of Spirifer cuspidatus is fully borne out by the 
examination of a remarkably well-preserved specimen of that 
type (No. 5), this result is in apparent contradiction to the fact 
that shells (Nos. 2, 3, 4) not externally distinguishable from it 
are indubitably perforated. The difficulty has been entirely re- 
moved, however, by an examination of the internal structure of 
these shells, the results of which are in complete harmony with 
