E. Wether eel — Organisms in Carboniferous Limestone. 535 



asked his opinion on them. He kindly wrote me as follows : " I think 

 3'our pentagonal stem-joints may not improbably be identical with those 

 figured by Miller on plate 2 of BJiodocrinus, figs. 17-22, but I have 

 great doubts whether they can be properly referred to BJiodocrinus." 



The microscopic section shown in Fig. 1 appears to throw some 

 light upon the apparent pentagonal joints. The central object re- 

 presents one of them surrounded by a circular margin. It is there- 

 fore possible that some of these Crinoids have a pentagonal centre, 

 and that it is this central portion which is represented on PL XV. 

 Fig. 12. I have shown my specimens to Mr. E. Etheridge, jun., who 

 informs me that he has observed the same thing in some Crinoids 

 which have come under his notice. 



Polyzoa. — The specimens of Polyzoa were sent to Mr. John 

 Young, Curator of the Hunterian Museum, Glasgow, who kindly 

 examined them for me. Though the Polyzoa occur in such large 

 numbers in the crinoidal bed, Mr. Young has only been able to detect 

 two genera and species, namely, Bhabdomeson (Millepora) gracile 

 (Phill.), and Fenestella tuberculocarinata (Etheridge, jun.). 



Mitcheldeania Nicholsoni, gen. et. sp. nov. (Plate XIV. Fig. 6). 

 — I have referred the specimens of this organism to Mr. John Young, 

 Dr. Hinde, Professor Nicholson of Aberdeen, and to Mr. Kobert 

 Etheridge, jun., all of whom have kindly examined them, but are 

 unable to recognize them as identical with any known form. I have, 

 therefore, determined to describe and figure it as a new provisional 

 genus under the name of Mitcheldeania, after the locality (Mitcheldean) 

 near which I found it. To Professor Nicholson I am especially 

 indebted for assistance in examining the fossil, but he is in no way 

 committed to any of my remarks in reference to it. As a slight 

 acknowledgment of Professor Nicholson's assistance and appreciation 

 of his work generally, I propose to name the first species of the 

 genus Nicholsoni. In working out this organism I have been placed 

 at a disadvantage in not being able to separate reliable specimens 

 from the matrix, on account of the nature of the rock in which the 

 fossil occurs ; the determination, therefore, has been chiefly arrived 

 at from microscopic slides. 



The organism, Fig. 6, consists of a series of concentrically arranged 

 layers, or laminae, penetrated by systems of tubuli which become 

 more minute and numerous in the central series of laminae. The 

 tubuli are separated by the skeleton fibre, which is itself penetrated 

 by a minute canal system. There are also other tubuli of larger 

 size than are seen in the inner laminae, which appear first in the third 

 series, and become more numerous outwards. The skeleton fibre 

 is also penetrated, in places, by centres of growth made up of 

 concentrically arranged minute tubuli, resembling the series which 

 constitute the nucleus of the entire organism. At the base there 

 is a peduncle which probably served for attachment. 



Conclusions. — Mitcheldeania Nicholsoni, then, was an organism the 

 structure of which consisted of a series of concentrically arranged layers 

 penetrated by two systems of tubuli, the larger measuring -003 and 

 the smaller -001 of an inch in diameter. The latter were probably 

 filled with living matter, and the larger I regard as zooidal tubes. I 



