DESCRIPTION OF SPECIES BRACHIOPODA 3l3 



CLEIOTHYRIS ROYSSI (L'Eveille) 

 Plate 14, figures 1-3 



1835. Spirifer de royssii L'Eveille, Memoires de la Societe Geologique de France, 



volume 2, page 39, plate 2, figures 18-20. 

 1859. Athyris royssii Davidson, British Fossil Brachiopoda, volume 2, page 84, 



plate 18, figures 1-11. 

 1887-. Athyris royssii De Koninck, Faune du Calcaire Carbonifere de la Bel- 



gique, part 6, page 85, plate 19, figures 19-28. 



Description. — Shell lenticular, the length somewhat less than the 

 width, the two valves subequally convex. Pedicle valve moderately con- 

 vex, the greatest depth a little posterior to the middle, the surface sloping 

 more abruptly to the cardinal margin; mesial portion of the valve 

 slightly flattened anteriorly and sometimes depressed in a slight, ill 

 defined sinus; the beak small, pointed, in close contact with the umbo of 

 the brachial valve. Brachial valve equally convex or sometimes slightly 

 more convex than the pedicle, the greatest depth near the center, the 

 mesial portion slightly flattened to meet the flattened portion of the 

 pedicle valve. Surface of both valves marked by fine, regular, concen- 

 tric, lamellose lines of growth, which, when the surface characters are 

 perfectly preserved, are produced into rows of close set concentric, imbri- 

 cating fringes of elongate, flattened spines. 



The dimensions of a nearly perfect individual are: Length, 18 milli- 

 meters; width, 21 millimeters; thickness, 9.5 millimeters. 



Remarks. — The name Athyris or Cleiotliyris royssii has not always 

 been correctly applied in America. These Fern Glen specimens, how- 

 ever, seem to be certainly specifically identical with this European species 

 as it has been interpreted by Davidson and De Koninck. As the shell 

 usually occurs, the concentric fringes of fine spines have been destroyed, 

 so that only concentric, sublamellose markings are preserved, although a 

 few examples have been observed which preserve in part the fringes of 

 spines. The species resembles C. hirsuta Hall, but it grows to a larger 

 size and is proportionally broader. It differs from C. sublamellosa Hall 

 in its more nearly equally convex valves, that species having the brachial 

 valve much more convex than the pedicle, and also in its greater propor- 

 tional width. 



CLEIOTHYRIS INCRASSATA Hall 



Plate 14, figures 8-10 



1858. Athyris mcrassatus Hall, Geology of Iowa, volume 1, part 2, page 600, 



plate 12, figure 6. 

 1895. Athyris incrassata H. & C, Paleontology of New York, volume 8, part 2, 



plate 46, figure 21 ; plate 83, figure 39. 

 XXVII— Bull. Geol. Soc. Am.. Vol. 20. 1908 



