BRITISH SILURIAN BRACHIOPODA. 91 



exposition of the internal characters of the whole class referred to ; and from being the 

 most obscure, this part of the palseontological field might thus become the most clear and 

 open. 



" It has been a great pleasure to me to work with Mr. Davidson. Widely acquainted 

 with all that was previously known on the subject, open to conviction, but exceedingly 

 careful in the trial of evidence, Mr. Davidson has given to my researches all the value that 

 was possible, and I feel persuaded that if any mistakes shall be ultimately found in the 

 results here recorded, these will be both few and slight." 



I may add that Mr. Glass has generously presented to me all the preparations which 

 he has made during this investigation, including forty-eight British and thirteen Foreign 

 species. 



Genus — Nucleospira, Davidson, 1881. 



3. Nucleospira pisum, Sow., sp. Dav., Sil. Mon., PI. X, figs. 16 — 20 ; and Sil. Sup., 



PI. IV, figs. 15 to 18. 



Nucleospira pisum, Bav. Geol. Mag., New Series, vol. viii, p. 7, 1881. 



At page 106 of my 'Silurian Monograph,' I fully described and illustrated the external 

 characters of this important and abundant Upper-Silurian species. I then also ascertained 

 that Nucleospira pisum was provided with spiral processes for the support of the labial 

 appendages, and that these may sometimes be seen through the transparency of its walls, 

 as in the specimen I figured in 1866. 



In the ' Twelfth Annual Report of the Regents of the University of the State of New 

 York,' Professor Hall devotes several pages to the description and illustration of his genus 

 Nucleospira. Since then the Rev. Norman Glass has, in the most careful and able 

 manner, developed the spirals in this small species, and, what is far more difficult, 

 its connecting processes. The spirals are somewhat oval in shape, and each spiral is 

 found to consist of not more than six or seven convolutions, the extremities of the spirals 

 being directed towards the lateral portions of the shell. The two principal stems of the 

 spiral coils are attached to the hinge-plate, and extend a little way into the interior of 

 the shell between the spirals, when they are suddenly bent backwards and upwards 

 towards the hinge before following the curve of the bottom of the dorsal valve. The 

 hook-shaped processes, which hang downwards from the hinge-plate, and which are 

 formed by the primary lamellae, are short and slightly bent inwards towards the ventral 

 valve, as in Merisfa, Meristella, Meristina, and Betzia. In Nucleospira and Athyris, how- 



