38 SUPPLEMENT TO THE 



preparation the primary coils of the spirals and the process connecting them were also 

 shown as a transparency. 



In our description of the species at p. 49 of the * Devonian Monograph ' we have 

 alluded to the differences in shape it assumes, as well as its variability in the number 

 of ribs that ornament its surface. In some examples there are but six large ribs in each 

 valve, the dorsal valve being as long as wide ; but in other specimens this same valve 

 becomes more and more transverse, and at the same time the ribs become smaller and 

 more numerous, passing thus into the variety muUiplicata, upon which as many as 

 twenty-two ribs may be counted on each valve (Dev. Sup., PI. II, fig. 8, 8 a, b, c). 



Besides the localities already named in the description of the species, I may mention 

 that Mr. Whidborne has found the shell in blackish shales at Hope's Nose, near Torquay, 

 where the inclination of the cleavage-planes has much distorted the fossils. Hope's 

 Nose is a very rich fossiliferous locality for Brachiopoda, but good and perfect specimens 

 with their natural shape are very uncommon there. 



In the Middle Devonian of the Oarstone, near Torquay, Mr. Whidborne found several 

 specimens of a small form of Cyrt'ma (Dev. Sup., PI. I, fig, 38), which he 

 believes to be distinct from C. heterocUta. It is smaller and more regular in shape, Avith 

 fewer and more rounded ribs, but it may be only a smaller variety of Defrance's species. 



Genus — Glassia, Dav., 1881. 



26. Glassia Whidbornei, Dav. Dev. Sup., PI. I, figs. 10 to 14. 



Shell elongated, oval, as long or longer than wide, nearly straight in front ; valves 

 moderately convex, ventral valve the deepest; beak incurved, with a small circular 

 foramen; surface smooth. 



Length 7, breadth 6, depth 1 line. 



In the interior of the dorsal valve the principal lamellae forming the first coils of the 

 spirals are, at a short distance from the attachment to the hinge-plate, connected together 

 by a ribbon-shaped lamella or loop. This loop, commencing on each side from the 

 principal lamellae, converges downwards in the shape of the letter V- The principal 

 coils of the spirals directly face the lateral margins. The ends of the spirals meet each 

 other in the centre of the shell. Each spiral consists of four coils. 



Ohs. — The discovery of this genus in the Devonian is entirely due to the Rev. 

 Norman Glass, who, while experimenting upon some small specimens sent to him by Mr. 

 G. P. Whidborne, was struck by the spirals presenting the same characters which he had 

 already discovered in the Silurian Glassia obovata and elongata ; and, having communi- 



