BRITISH DEVONIAN BRACHIOPODA. 25 



developed by the Rev. N. Glass, but from want of sufficient material he vi^as unable to 

 expose their attachments. The compressed shape of the shell and absence of fold and 

 sinus distinguish it from A. concentrica, and it is with much pleasure that I name it 

 after the Rev. Norman Glass, who was the first to determine its generic position. 



12. Athyris concentrica, Von Buch, sp. Dav., Dev. Mon., PI. ITI, figs. 11 — 15, 



24 ; and Dev. Sup., PI. I, figs. 23, 



4; PI. II, figs. 10, 10a. 



The external characters of this species have been given at page 15 of my Devonian 

 Monograph, and need not be repeated. The shell varies with age, and the var. lamellosa 

 is in all probability a young condition of the full-grown A. concentrica. As the shell 

 acquires age the concentric equi-distaut ridges that ornament its surface become, com- 

 paratively speaking, much less marked than, in young individuals, and are sometimes 

 hardly visible in very adult individuals, such as in some of those we find at Ferques, near 

 Boulogne-sur-Mer. 



Many years ago, in 1 842, Mr. Bouchard and myself found at Ferques some weathered 

 specimens ^i A. concentrica, showing the spirals in a very beautiful and perfect condition. 

 We also found two examples showing the hinge-plate, and close to the extremity of the 

 umbo a small circular aperture communicating with a circular curved tube, which I have 

 already described and illustrated in PI. VI, fig. Qi^^ of my Introduction to the first 

 volume of my Monograph ; but none of the Ferques specimens showed either the attach- 

 ments of the principal stems of the spirals to the hinge-plate or the connecting processes 

 or loop. 



In 1871, in the Atlas to his ' Brachiopoden (Petrefactenkunde Deutschlands),' 

 tab, 51, 1871, Quenstedt gives several figures in which he represents the accessory 

 lamella and the loop, but not quite clearly nor completely, although he has evidently 

 devoted much attention to the subject and very nearly got the different parts complete- 

 Quenstedt does not, however, give any figure of the attachments to the hinge-plate. 



In A. concentrica the convolutions of the spirals are numerous and rather close to 

 each other ; and in a specimen measuring an inch in breadth I counted fifteen coils in each 

 spiral. The spirals are closer together on the ventral than on the dorsal side. 



We are indebted to the Rev. Norman Glass for a complete knowledge of the shape 

 of the loop and the attachments of the principal stems of the spirals to the hinge-plate. 

 After several more or less unsuccessful attempts on specimens from Lummaton he was 

 enabled to develop the loop and other attachments in a very complete and satisfactory 



4 



