62 
PALEONTOLOGY OF NEW YORK. 
The differences from other meristelloids are sufficient to justify the separa¬ 
tion of this species, with which we are at present able to associate only the 
form described by Mr. Billings as Athijris Junia, from the Anticosti group, 
Divisions 2-4.* 
Genus DAYIA, Davidson. 1881. 
PLATE LV. 
1839. Terebratula, J. de C. Sowerby. Murchison’s Silurian System, pi. v, tig. 7. 
1846. Atrypa, McCoy. Synox^sis Silurian Fossils of Ireland, p. 40. 
1847. Tei'ebratula, Barrandb. Silur. Bi-achiopoden aus Bohmen, pi. xv, fig. 4. 
1848. Terebratula, Davidson. Bull. Soc. Geol. de Fi-ance, sec. ser., vol. v, jd. 328. 
1848. Hypothyris, Phillips. Mem. Geol. Survey Great Britain, ji. 281. 
18.62. Hemitliyris, McCoy. British Palseozoic Fossils, ji. 204. 
1859. Mhynchonella, Salter. Murchison’s Siluria, second ed., ji. 545, pi. xxii, fig. 12, 
1860. Mhynchonella, Lindstrom. Gotlands Brachioxioder, x^- 381. 
1869. Mhynchonella f, Davidson. British Silurian Brachiopoda, xi. 190, pi. xxii, figs. 20-23. 
1881. Dayia, Davidson. Geological Magazine, new ser., vol. viii, p. 291. 
1882. Dayia, Davidson. Biatish Silurian Brachiopoda, Sux'ixilement, 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,:!: 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 
* Catalogues Silurian Fossils of Aiiiicosli, i). 46. 1866. 
t British Silurian Brachioxioda, p. 190, xil. xxii, figs. 20-23. 
t 1881 and 1882, as cited. 
