BRITISH SILURIAN BRACHIOPODA. 213 



Genus — Acrotreta, Kutorga, 1848. 



152. Acrotreta Nicholson:, Bav. Sil. Men., PI. XLIX, figs. 30—34 ; Sil. Sup., 



PL XVI, figs. 21—23. 



At p. 348 of my ' Silurian Monograph ' I described and figured a series of specimens 

 of this species from the black shales of the Upper Llandeilo beds of Dobbs Linn, near 

 MofiFat, in Dumfriesshire. Since then Mrs. R. Gray has found the same fossil in 

 some abundance in the Llandeilo at Craighead, Ardmillan Brae, and Balcletchie, in the 

 Girvan district of Ayrshire. The specimens are larger and the ventral valve deeper and 

 more pyramidal than in those that have passed through my hands from Mofiat. I have 

 therefore added a series of figures to more fully illustrate the characters of the species. 

 Mrs. R. Gray's largest examples of the ventral valve measured 5 lines in length by 

 about the same in breadth. 



In his paper on the " Silurian Rocks of the County Down, Ireland " (' Proceedings of 

 the Belfast Natural History Club,' Appendix for 1876—77), Mr. W. Swanston states to 

 have found A. Nicholsoni at Coal-Pit Bay, County Down, Ireland. 



153. Acrotreta? costata, Dav. Sil. Sup., PI, XVI, fig. 24. 



Shell small; dorsal valve semicircular, 1^ lines in length by about the same in 

 breadth. Ventral valve pyramidal, 2 lines in length, extremely truncated by a small 

 circular foramen, area triangular, large in proportion to the size of the specimen. 

 Surface of valve bears a few comparatively strong ribs. 



Ois. — One specimen only was found by Mrs. R. Gray in the Llandeilo at Balcletchie, 

 Girvan, Ayrshire. It very nearly resembles Acrotreta Nicholsoni in size and shape but 

 differs from it by its costse or ribs. 



Genus — Acrothele, Linnarsson, 1875. 



In his valuable paper on the " Brachiopods of the Paradoxides-beds of Sweden " 

 (' Bihang till k. Svenska Vet. Akad. Handlingar,' Band 3, 1876), also in his memoir ' Om 

 Paunan i Kalken Sveriges geologiska Undersokning,' p. 25, pi. iii, 1870, Prof. G. 



