62 PALEONTOLOGY OF NEW YORK. 



The differences from other ineristelloids are sufficient to justify the separa- 

 tion of this species, witli which we are at present able to associate only the 

 form described by Mr. Billings as Athyris Junta, from the Anticosti group, 

 Divisions 2-4* 



Gends DAYIA, Davidson. 1881. 



PLATE LV. 



1839. Tgnbratula, i. db C. Sowbbby. Murchison's Silurian System, pi. v, fig-. 7. 



1848. Atrypa, McCoy. Synopsis Silurian Fossils of Ireland, p. 40. 



1847. Ter^ralula, Barbandk. Silur. Brachiopoden aus BOhmen, pi. xv, tig. 4. 



1848. Tertbratula, Davidson. Bull. Soc. Geol. de France, sec. ser., vol. v, pi. 328. 

 184S. HypothyrU, Phillips. Mem. Qeol. Survey Great Britain, p. 281. 



1852. HemithyrU, HcCot. British Palaeozoic Fossils, p. 204. 



1859. Rhyndumella, Saltkr. Murchison's Siluria, second ed., p. 545, pi. xxii, fig. 12, 



1860. Rhynchonella, Lindstb5m. Gotlands Brachiopoder, p. 381. 



1869. Rhynclumellaf, Davidson. British Silurian Bi-achiopoda, p. 190, pi. xxii, tigs. 20-23. 



1881. Dayla, Davidson. Geological Magazine, new ser., vol. viii, p. 291. 



1882. Dayia, Davidson. British Silurian Bracbiopoda, Su})plement, p. 96, pi. v, figs. 1-4. 



Mr. Davidson has established this genus upon the little species, Terebratula 

 navicula, J. de C. Sowerby, from the Wenlock and Ludlow formations of Great 

 Britain and the Island of Gotland. In his earliest description he referred the 

 species with doubt to Rhynchonella,! and at that time gave an elaborately 

 illustrated account of the peculiar interior surface characters of the valves. 

 Subsequently, J ascertaining from the preparations of the brachidium made by 

 the Rev. Mr. Glass, the distinctive structure of the loop, he proposed it as the 

 type of a new generic division. 



The shells of this species are small, subtrihedral in contour, with a very 

 convex pedicle-valve which may be obscurely keeled along the middle and de- 

 pressed laterally ; and a brachial valve which is convex posteriorly, but 

 becomes concave over the anterior region, and bears a well developed median 

 sinus. The hinge-line is short ; the cardinal area absent. The umbo of the 

 pedicle-valve is gibbous and its apex closely incurved, concealing the foramen. 

 Deltidial plates were probably developed but they appear to be invariably lost 

 in separated valves. The delthyrium is wide, the teeth divergent, moderately 

 conspicuous and unsupported by lamellae. In the bottom of the valve are two 



* Oataloguea Silurian Kosidla of Aulicusti, p. 46. 1866. 

 t Britisb SiluHan Bracbinpo<la, p. 190, pi. xxii, figs. 20-23. 

 I 1881 and 1882, as cited. 



