Tylothyris mesacostalis (Hall, 1867)

Fig. 4E.

Spirifer mesacostalis; Hall 1867: 240, pl. 40: 1, 2, 4–13; Hall and Clarke 1894: 16, 35, pl. 34: 32–34.

Tylothyris mesacostalis (Hall, 1867); Cooper 1944: 321–322, pl. 122: 20, 21; Linsley 1994: 234, pl. 127: 6–20.

Material.—Figured specimen NYSM 15711, and approximately 180 additional unnumbered specimens on parts and counterparts of split slabs.

Remarks.—This is a long ranging species in the Late Devonian of New York. It is the nominal species of Dutro’s (1981: 78, figs. 2, 7) middle Frasnian Tylothyris mesacostalis Assemblage Zone. Its range in the New York Upper Devonian is shown to begin in the upper part of the Sonyea Group (mid Frasnian) and terminates in the Conneaut Group at the top of the interval of Dutro’s (1981: figs. 2, 7) Famennian Spinulicosta arctirostrata Assemblage Zone.