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Map point data provided by iDigBio.
- C3 Sequence (Mount Auburn, Corryville)
- C2 Sequence (Bellevue, Fairview: Fairmount, Mount Hope)
- C1 Sequence (Clays Ferry/Kope: McMicken, Southgate, Economy/Fulton)
Identification in Hand Sample
Ctenodonta perminuta from the Liberty Formation of Brookville, Indiana (OUIP 2202)
Fossils of Ohio (1996):
- Shell elongate
- The Middle Ordovician genus Ctenodonta is represented by C. perminuta Foerste, a small ovate species that has the beaks near the anterior margin and numerous subequal teeth in the hinge.
- The species (C. perminuta) ranges, according to Bassler’s Index, from the Eden to the Maysville and is known from Cincinnati and vicinity. In New York we have found the species quite common at station 14 of the Whetstone gulf section and at the outcrop in the bank of the river, 2 miles below Pulaski; where it is associated with Arthropora cincinnatiensis (James). In both localities it is common.
- While Ulrich’s material consisted of casts of the interior only, ours is largely made up of shells preserving the exterior. It is seen by these that the exterior was nearly smooth, only faint growth-lines being visible, under the lens, near the basal margin, which are threadlike or raised, as in C. filistriata and C. lorrainensis.
- The majority of our specimens are slightly larger than the type material, the average height reaching 2 mm and a few even attaining height which is double that given by Doctor Ulrich.
- Shell very small, commonly about 1.5 mm. in length and 1.15 mm. in height, widest anteriorly; anterior outline rounded below, generally nearly vertical in the upper half, and subangular in the antero-cardinal region; basal margin broadly convex, posterior end obliquely truncate, strongly rounded in the lower half. The species is known from casts of the interior only. In these the beaks are prominent, moderately incurved, and situated between one-fourth and one-third of the entire length behind the anterior extremity. The muscular impressions are unusually distinct for so small a shell, and the structure of the hinge seems to have been very much as in C. levata, Hall, sp., and other forms of that section of the genus.
- The extreme minuteness of the shell and the comparative strength of the muscular attachments will distinguish this form at once from all other species of the genus having a similar shape. The C. oblique Hall, sp., another minute species of the Cincinnati rocks, and of which the recently proposed Palaeoconcha faberi (S.A. Miller, 1892, N. A. Geol. And Pal., p. 498), seems to me to be a synonym, is a higher shell and doubtless belongs to quite a different section of the genus, being closely related to such forms as C. compressa Ulrich and C. astariaeformis Salter.
- Formation and Locality: Lower and middle beds of the Cincinnati group, Cincinnati, Ohio.