2 Thomas Davidson — Spiral-Bearing BracJiiopoda. 



Ml'. Whitefield have also been engaged in developing tlie spirals and 

 their connections in the Palaeozoic Brachiopoda, but only in American 

 specimens, and principally in siliceous shells, or in shells possessing 

 a hard limestone matrix. Mr. Glass's operations, however, have 

 been confined almost entirely to English specimens, and, as it will 

 presently appear, to those English specimens only which were partly 

 or wholly filled with spai*. Having myself most carefully studied 

 and drawn Mr. Glass's prepared specimens I am able to assert that 

 they do not admit of doubt or inisconception, and that they com- 

 pletely obviate the necessity of restoration — a process which must 

 always be associated with some degree of uncertainty. 



In my Carboniferous Supplement published by the Palaeonto- 

 gi'aphical Society at the commencement of 1880, I gave a brief 

 account of Mr. Glass's discovery, accompanied by figures and de- 

 scriptions of the spirals of no less than thirteen species of Carbon- 

 iferous Spirifera and Athyris — all of them having been worked out 

 by the new process. Since the preparations for the publication of 

 the above supplement were completed Mr. Glass has been engaged 

 in investigating not only the spirals, but also their connections 

 in the shells of the Upper Silurian formation, and also in the Car- 

 boniferous shells of the genus Athyris. Mr. Glass had informed me 

 previously that his process was unsuitable for developing the con- 

 necting lamellae of the spirals. He has proved, however, by more 

 recent researches, and even beyond his own expectations, that it is 

 eminently adapted for that purpose. 



The new process discovered by Mr. Glass simply applies to those 

 shells which are partly or wholly filled with spar. In all the pre- 

 parations that were figured in the Carboniferous Supplement the 

 spirals were shown in their sparry matrix opaquely, but this method 

 vp^ould have been very difficult in developing the spii'als in the small 

 Silurian Brachiopods, and would have been entirely useless in 

 revealing their connecting lamellee. Mr. Glass, indeed, except in 

 one or two instances, was unable to show the connections of the 

 spirals opaquely even in the larger specimens. However, that 

 which could not be shown opaquely has been successfully developed 

 by means of transparency. When the shells have been found 

 wholly filled with spar, both valves have been removed, and the 

 sparry matrix scraped away on either side until the spirals were 

 clearly to be seen by holding the specimen up against the light. In 

 order to show the connections of the spirals, not only the matrix 

 surrounding the spirals, but also parts of the spirals themselves, 

 have had to be scraped away in vai'ious directions. As I remarked 

 in my Carboniferous Supplement, previously to the discovery of 

 Mr. Glass's process our knowledge of the spirals of the Palaeozoic 

 Brachiopoda depended upon the rare chance of finding empty shells 

 in which these appendages were naturally preserved, or upon the 

 equally rare chance of finding specimens in which the shell and 

 spirals were silicified so that the latter might be developed by the 

 use of diluted acid. In addition to these means of obtaining know- 

 ledge in relation to the spirals, there was only the difficult and 



