THE BEACHIOPOi)A. 49 



55. — Terebratula cortonensis, S.S. Buchnan. 



1873. Terebkatula ovoides, E. Beslongschamps (non Sowerby), 

 Bracli. Jurassiques, plate 61, figures (1-3?) 

 5, 6, 8, and 9. 



Syn? 1867. Terehratida Buehnani, Waagen Geogn. Paliiont. 

 Beitriige, page 637 (131), No. 155. 



This species varies slightly in shape, when the front view is 

 considered. It is more or less oval, the broadest part being 

 sometimes about the middle of the smaller valve, and sometimes 

 a little below it. Dorsal valve rather flat, ventral or larger valve 

 somewhat convex. The base is not biplicated, but is slightly 

 raised in front. The margin line also, at the side, is well 

 recurved, and this is a constant character in this species. The 

 beak projects forward, rather beyond the dorsal valve, and is 

 ciirved. The foramen is oval, rather large, and nearly touches 

 the smaller valve. 



This is a peculiar species, occupying as it were a position inter- 

 mediate between the variations of several other species. It 

 approaches Terebratula punctata variety Haresfieldensis, but is 

 distinguished from it by greater proportionate breadth, much 

 flatter dorsal valve, recurved side margin, and beak projecting 

 beyond the dorsal valve. It also approaches Terel. Buehnani and 

 young Tereh. perovalis, but is much shorter, broader, and more 

 circular in shape than the first and lacks the biplications of the 

 second. 



Our specimens agree best with figures 5 and 8a of Deslongs- 

 champs' plate, but generally have their greatest breadth rather 

 lower down, and the base consequently more rounded. The fold is 

 also not often so much raised as shewn in figure 8b. Whether 

 figures 1-3 are really the young or not I am at present unable to 

 say. 



Terebratula cortonensis generally occurs in the zone of Sowerbyi, 

 but I believe that it begins in the zone of Murchisonto. E. 

 Deslong<5hampB says that it fTer. ovoides J occurs in the infra-oolitic 

 marls. 



