BRITISH SILURIAN BRACHIOPODA. 



117 



their arrangement to those of any other spiral-bearing species with which he was 



acquainted, and at once forwarded to me his jfirst developed specimens. So interesting 



and new did they appear to both of us that no labour or pains were spared by Mr. 



Maw in procuring more specimens, or by Mr. Glass in working on them — a most 

 difficult process, on account of their complicated details, and requiring great patience, 

 skill, and experience. 



I? A 



Olassia ohovata. Prepared by the Rev. Norman Glass. Seen as a transparency. 

 A. Dorsal ; B. Ventral valve view. 



Externally the shell of Glassia obovata is small, rarely attaining with us quite five 

 lines in length, by six in breath and three in depth. It is marginally circular, straight, 

 rounded, or sHghtly indented in front ; beak small, incurved ; surface smooth. In the 

 interior of the dorsal valve there are spirals 

 for the support of the lateral or brachial 

 appendages. 



The principal lamellae forming the first 

 coils are, at a short distance from the attach- 

 ment to the hinge-plate, connected together 

 by a riband-shaped lamella or loop (as in 

 Atrypa). This lamella, commencing on each 

 side from the principal coil, converges down- 

 wards in the shape of the letter V (figs, a and 

 c), and its two extremities are sometimes 

 turned very slightly 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- 

 pressed and oval shape, together with the distance that always occurs between the base 

 of the spirals and the lateral margins, allows the necessary room for the first convolutions. 



C. An outline sketch of the arrangement of spiral 

 coils in Olassia ohovata\eViivs\ aspect, restored, from 

 specimens developed by the Rev. N. Glass. The dor- 

 sal side of the coils in each spiral cone is somewhat 

 displaced from its natural position in order to show 

 the continuity of the coils. E, edge view of a spiral; 

 V, ventral ; D, dorsal. 



