Thomas Davidson — Spiral-Bearing Brachiopodd. 11 



breadth, by tbree in depth, with nearly a flat or even slightly concave 

 dorsal valve. Still, notwithstanding its small dimensions, after 

 endless trouble Mr. Glass has succeeded in exposing in four specimens, 

 and in the most complete manner possible, its spirals and their 

 connecting process. These in the main agree pretty closel}^ 

 although differing slightly in detail, with those of Atrypa marginalis, 

 and Mr. Glass's specimens show that soon after the principal stems 

 of the spirals leave their attachment to the hinge-plate, they give off 

 a V-shaped lamella, by which they become connected, as in Atrypa. 

 Fig. 11. Fig. 12. 



Atrypa Barrandi, Dav., developed by E.ev. N. Glass. 

 The principal coils however are not quite level, as in Atrypa. The 

 two inner sides of these coils being slightly higher than the two 

 outer sides, and turned towards the margin of the shell. The ends 

 of the spires curl over to meet each other, but the amount of con- 

 vexity on the side facing the bottom of the dorsal valve is very 

 slight, because there are but four or five convolutions, and this 

 slightness of convexity is necessitated by the very small depth of 

 the valve. I tlierefore believe that the spiral arrangement in 

 A. Barrandi is only a modification of that of Atrypa reticularis and 

 A. marginalis, and with which genus A. Barrandi should be classed. 



Genus Glassia, genus nov. 

 Type Glassia [Atrypa) ohovata, Sow., Sil. Syst., pi. viii. fig. 9, 1839. 

 Shell marginally circular, transversely or longitudinally oval, 

 rounded or slightly indented in front. In the interior of the dorsal 

 valve there are spiral coils for the support of the labial or brachial 

 appendages. The principal lamellae forming the first coils are at a 

 short distance from the attachment of the hinge-plate connected 

 together by a riband-shaped lamella or loop (as in Atrypa). This 

 lamella, commencing on either side from the principal coils, converges 

 downwards in the shape of the letter V (Fig- 14), and its two ex- 

 tremities are sometimes slightly turned upwards before uniting. 

 The principal coils directly face the lateral margins. The ends of the 

 spirals meet each other in the centre of the shell, and their close 

 apposition sometimes serves to depress and thicken the end of the 

 spirals and to conceal the final coil on either side. The spirals, which 

 consist of from four to five coils, are compressed, and their com- 



