Thomas Davidson — Spiral- Bearing Brachiopoda. 3 



generally unsatisfactory method of making sections of the hard 

 limestone matrix by which the sliells were usually filled. Now, 

 however, and by Mr. Glass's process, there is nothing in relation to 

 the spirals or their connecting lamellEe in the Carboniferous and 

 Silurian Brachiopoda that may not Avith time and patience be dis- 

 covered. Mr. Glass has ascertained that many shells partly or 

 wholly filled with spar are met with belonging to nearly every 

 species, and whilst it is true that in a large proportion of these the 

 spirals are either absent, fragmentary, or broken from the hinge- 

 plate and displaced, yet specimens having all the required conditions 

 do occasionally occur, and there is nothing to prevent a complete and 

 satisfactory investigation. 



As I have already said, there can be no mistake as to the certainty 

 of the results attainable under this process. When the spirals are 

 met with in the sparry matrix of the shell either in a fragmentary 

 condition, or broken from the hinge-plate and displaced, there may 

 be, and there frequently are, very confusing and doubtful appearances, 

 but as soon as the spirals are found in a perfect condition, all that 

 was before confusing and doubtful becomes clear and certain. This 

 more especially applies to mature shells, for in younger specimens, 

 even when otherwise perfect, it is sometimes difficult to get a clear 

 conception of the spirals, arising from their not having assumed 

 their normal shape and position in the shell. In the case just 

 supposed, where under the new process clear and certain results 

 have been obtained, the whole of the spirals either on the dorsal or 

 ventral side, or the whole of the connecting process in its relations 

 to the spirals, is seen, either opaquely or transparently in situ and 

 at once, and not a bit at a time, as is the ca;se where the spirals, etc., 

 are endeavoured to be ascertained by the cutting of sections. This 

 Mr. Glass thinks is a great disadvantage in the use of sections as 

 compai'ed with his process — a disadvantage greatly increased, as it 

 seems to him, when the sections are not made through a sparry 

 matrix which shows the lines of the spirals, etc., in relief, but 

 tlirough a hard earthy limestone, in which the lines are difficult to 

 trace through their similarity of colour to the matrix. For the 

 details of Mr. Glass's new process, in which hydrochloric acid is 

 an indispensable agent, readers are referred to my Carboniferous 

 Supplement, and also to the forthcoming Silurian Supplement, which 

 will contain a more full account prepared by Mr. Glass at my request. 



In 186G, when px'eparing my Silurian Monograph, I found it quite 

 impossible to procure specimens of the spiral-bearing species of the 

 British Silurian Brachiopoda showing more than a very incomplete 

 indication of their internal processes, nor was it possible for me to 

 develope them on account of the hard matrix which filled the shell. 

 Since then, thanks to Mr. Glass's great skill, I can now furnish figures 

 showing the complete spirals, the attachment to the hinge-plate, and 

 in most cases the connecting pi'ocesses of Spirifera plicateJla, Sp. 

 crispa, Cijrtia exporrecta, Meristella tumida, II. didijma, Nudeospira 

 jnsum, Betzia Salteri, Atrypa reticularis, A. marginalis, A. Barrandi, 

 Glassia obovata and G. elongata, all worked out in their completed 



