zFormerly: Rhynchonella perlamellosa
- 1882 Rhynchonella perlamellosa Whitfield, Geol. Wisconsin, 4, p. 265, pl. 12, figs. 23-25.
- 1924 Rhynchotrema perlamellosum Foerste, Upper Ordovician faunas in Ontario and Quebec, p. 125-126, pl. 11, fig. 5a-b.
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Map point data provided by iDigBio.
- C6 Sequence (Elkhorn)
- C5 Sequence (Whitewater, Liberty, Waynesville)
Identification in Hand Sample
- Medium sized brachiopod
- Subangular, radiating plications – 6-8 on each side of the shell
- Fold on the ventral valve and sulcus on the dorsal valve
- 4 plications on fold; 3 plications on sulcus
- Coarse, strongly lamellose growth lines – highly defined
- Growth lines arch backwards and cross plications
- Commisure “zig-zags” to follow fold and sulcus
- Tend to be almost circular in overall appearance
- Articulate brachiopod. Differs from the previous species in characteristics of the shell interior, but it tends to be larger than the previous species and to have more distinct growth lines. Entire Richmondian, except the Arnheim.
- Typical Specimens. Valves, through strongly convex, not gibbous or gerontic. Along lateral margins, the line of junction between valves somewhat angular. Concentric striae commonly more distinct and at greater intervals than in typical R. capax. The types were figured by Whitfield from the Richmond of Delafield and Iron Ridge, Wisconsin. Here the Fernvale type of the Richmond occurs, carrying a fauna quite distinct from any part of the Richmond in Ohio, Indiana, and Kentucky. The Fernvale fauna has not been found in Ontario or Quebec.
- Waynesville Specimens. In the Waynesville of Ohio, Indiana, and Kentucky, is a form, usually identified as Rhynchotrema capax, resembling R. perlamellosum in more moderate convexity and in more prominent and more distant concentric striae. Compared with the types of R. perlamellosum figured by Whitfield, the valves of the Waynesville specimens are more convex, but similar more convex specimens are known from the Fernvale in the Mississippi valley.
- The Canadian specimens resemble these Waynesville specimens more than they resemble the typical R. capax of the Whitewater member and hence are referred to this species provisionally
- Locality and Horizon. On Manitoulin island, the species of Rhynchotrema resembling R. perlamellosum occurs in the Meaford member northwest of Kagawong. Common in the Stromatocerium and Coral reef at the base of the Kagawong division of the Richmond, at Gore Bay (No. 8511), near Kagawong, and west of the Indian village 3 miles southwest of Little Current. Northwest of Manitoulin island it occurs also farther up in the Kagawong member.
- No specimen of Rhynchotrema has been found in the Richmond either south of Georgian bay or north of Lake Ontario.
- In Quebec, R. perlamellosum occurs in the lower Waynesville, St. Hilaire.
- Shell of a medium size, triangularly-orbicular or very broadly ovate in outline, and lenticular to ventricose in profile; Beak small, flattened and closely incurved; cardinal slopes convex and full, never depressed or excavated. Dorsal valve with a moderately elevated mesial fold extending nearly to the beak and the ventral with a corresponding sinus. Surface marked by strong, simple, subangular plications, four of which are elevated to form the fold and three depressed in the sinus, while from six to eight occur on each side of the shell; plications crossed by rather coarse, distant, strongly lamellose lines of growth, strongly arching backwards in crossing the plications, and continuing across the cardinal slopes to the margin of the shell with but slight diminution in strength.