12 



Thomas Davidson — Sjjiral- Bearing Brachiopoda. 



pressed and oval shape, together with the distance which always 

 occurs between the base of the spirals and the lateral margins, 

 Fig. 13. Fig. 14. 



Glassia obovata, Davidson ; developed by Rev. N. Glass. 

 allows the necessary room for the first convolutions. The dorsal 

 side of the spirals is flattened, whilst the ventral side is somewhat 

 ventricose. The spirals are closer anteriorly, but broader on the 

 posterior side, and the principal coils on the posterior side of the 

 spirals are slightly notched or indented, the notch or indentation 

 being in the direction of the end of the spiral. The posterior space 

 between the spirals is not as wide as the anterior space. 



The discovery of this new genus, as well as of all its interior 

 characters, is entirely due to the indefatigable exertions and perse- 

 vering research of the Eev. Norman Glass, who, after many trials 

 and endless trouble and patience, was enabled gradually to develop 

 the spiral coils, their mode of attachment to the hinge-plate and their 

 connecting process in the clearest and most unmistakable manner. 

 I have therefore much pleasure in naming this genus after its 

 discoverer. 



The shells belonging to the genus Glassia are small, and both 

 Glassia obovata and Glassia elongata, another species discovered by 

 Mr. Glass, are common to the " Buildwas beds " (Lower Wenlock 



Shales), but do not occur in any great 

 number. 



The genus Glassia unquestionably 

 belongs to the family Atrypidcg, al- 

 though it differs materially from both 

 Atrypa and Zygospira. 



Of Zygospira, Hall, we have not 

 hitherto discovered any specimens in 

 our English Silurian rocks. Prof. 

 Hall states that its spires are nearly 

 the same as in Atrypa, but differing 

 in the presence of a strong loop or 

 band which does not correspond in 

 shape, position or character with the 

 Zi/ffospira modesta, a.itei Hall. loop in Atrypa. 



Fig. 15. 



