DAVIDSON — SCOTTISH CAEBONIFEEOUS BEACHIOPODA. 



15 



tlie hinge side, but are wide apart in front. The liinge-plate is divided into 

 two portions, to which the principal stems are attached, and in the notch under 

 the extremity of the umbonal beak there exists a calcareous projection, to 

 which the term "cardinal" process has been applied, and to which was attached 

 one of the extremities of the di^■aricator muscle. A little lower down, on the 

 bottom of the valve, are seen four large elongated impressions, produced by 

 the adductor, and which hare been recently designated as the anterior and pos- 

 terior occlusor muscles by ]\Ir. Hancock. 



Lign, 4. — Interior of Athyris ambigua, shelving the spiral appendages. 



Lig-n. 5. — Interior of the dorsal valve of Spirifera striata. 



All the species referred to the genus Sjnrifera proper possess a fibrous non- 

 perforated shell-structure. 



The species of carboiuferous Spirifera that appear to have been hitherto dis- 

 covered in Scotland, are not so numerous as those of England or of Ireland ; 

 and, after a careful examination of many specimens, I coidd determine with 

 certainty but the nine following : — Sp. duplicicosta, Sp. hisidcata^ Sp. trigonalis. 



