Spirifer cuspidatus and of certain allied Spiriferidae. 71 



incli 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 fx-agment 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 

 "impunctate 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 palaeontologists 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. 



3. 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 pei'- 

 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 ofi", all the fragments first examined 

 having chanced to be imjDcrforate. 



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 imperforate. 



Thus, then, whilst my previous determination of the imper- 

 forate structure of Spirifer cuspidatus is fully borne out by tlie 

 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 



