4 Thomas Davidson — Spiral-Bearing Brachiopoda. 



shape by Mr. Glass, and showing what can be achieved by his new 

 process. All these perfect interiors will be fully described and 

 illustrated in my Silurian Supplement. 



In these investigatious it has been clearly shown that the spiral- 

 bearing Brachiopoda can be grouped according to the way in which 

 the spirals are connected. 



1. Spirifekid^. Spirifera, Spiriferina, Cyrtia, Cyrtina. 



2. AxHYRiDiE, Athyris, Meristella, Merista, etc. 



3. NucLEOSPiKiDiE, Nucleospiru, Betzia, Trematospira. 



4. Atrypid^, Atrypa, Goelospira, Zygospira, Glassia. 



I will now endeavour briefly to show the different characters pre- 

 sented in these groups from preparations developed b}'^ Mr. Glass, 

 and principally from British Silurian specimens. These results are 

 of the highest importance, for no good classification can be founded 

 on external characters only, and the interior arrangements are by far 

 the surest guides. 



SpiRIPEKIDiE, King, 1850. 



The spirals of Spirifera, Spiriferina, Cyrtia and Oyrt'na, are all 

 now well known. Mr. Glass worked out those belonging to Spiri- 

 fera pUcatella, Sp. crispa and Cyrtia exporrecta, in a very beautiful 

 manner. We are not yet, however, acquainted with the shape of the 

 lamella (which in all probability connected the two principal stems 

 YiQ, 1, of the spirals) in any of the Spirifei'idas except 



Spiriferina, but I hope that Mr. Glass before long 

 will be able to make this matter clear. 



In 1851, I fully described and illustrated the 

 spiral appendages of Spiriferina, their simple mode 

 of attachment to the hinge-plate, as well as the 

 position and shape of the semicircular lamella a, 

 which connected the two spiral coils. I also 

 showed that short spines projected from the spiral 

 lamellae on those parts that faced the front and 

 lateral portions of the shell. This last-named 

 S2nriferina rostrata. feature has been well shown by Mr. Glass to 

 occur also in Athyris planosulcata and Atrypa marginalis. 



ATHYRiDiE, Phillips, 1841. 



This division of spiral -bearing Brachiopoda comprises several 

 genera such as Athyris, Merista, and Meristella. 



Genus Athyris, McCoy = Spirigera, D'Orb. 



The internal characters of this important genus are now well 

 known. The finding by Mr. Howse of a perfect empty interior of 

 the dorsal valve of A. pectinifera enabled me to describe and illus- 

 trate, in a very complete manner, the shape of the spiral appendages, 

 their mode of attachment to the hinge-plate, as well as the comi^li- 

 cated system of lamellce by which the two first stems of the 

 spirals were connected. Again, in pi. xvii. of my Carboniferous 



