THE GEOLOGIST 
MARCH, 1859. 
PAL^ONTOLOGICAL NOTES ON THE BRACHIOPODA. 
By Thomas Davidson, Esq., F.R.S., F.G.S., etc. 
No. 2. On the Families STBOPHOMENiDiE and Productid^. 
In my last communication, I endeavoured to lay before the reader 
all the more important facts, already acquired, relative to the genera 
and sub-genera that are provided with spiral appendages for the 
support of the oral arms ; * and at the same time I referred to 
several points which still required to be elucidated and explained 
before the subject could be considered to have been satisfactorily 
studied. 
In, a note at the conclusion of that paper, allusion was made to a 
well-preserved internal cast of Cyrtina septosa, of which I now offer 
a representation, as it will show that the muscular impressions in the 
smaller or dorsal valve are similarly arranged to those of Spirifera, 
and that there does not exist in that valve any septa, as in Pen- 
tamerus ; the resemblance to the last-named genus being merely in 
the disposition of the median septum, and of the converging dental 
or rostral plates of the larger or ventral valve. 
I may likewise mention, before commencing the subject of the 
present communication, that, although the muscular impressions in 
the larger or ventral valve of Athyris or Spirigera are generally well 
* The Geologist, vol. i. p. 409. 1858. This paper has been translated into 
French by my friend Professor L. de Koninck, and will be published in the 
Transactions of the Royal Society of Liege, for 1859. 
VOL. II. H 
