Austinella is an extinct genus of stationary, epifaunal suspension feeders
Identification in Hand Sample:
- Subequally biconvex, unisulcate, ramicostellate with sporadic aditicules, strongly filate
- Ventral interarea long, curved, anacline dorsal interarea short, plane
- Ventral muscle scar with thickened margin
- Dorsal adductor scar subequally quadripartite
- Sub-rectangular ventral muscle field and Dinorthis-like cardinalia
Treatise on Invertebrate Paleontology, Part H, Vol. 3 (2000):
- Subequally biconvex, unisulcate, ramicostellate with sporadic aditicules, strongly filate; ventral interarea long, curved, anacline dorsal interarea short, plane; ventral muscle scar with thickened margin; dorsal adductor scar subequally quadripartite.
- This genus was originally given rather informal designation as a subgenus of Plectorthis by Foerste (1909, p.224). He gave no clear description, merely stating that it was typified by Orthis kankakensis McChesney and included O. whitfieldi Winchell. Although this statement established A. kankakensis as the nominal type species, later Foerste (1912, p.130) erroneously designed A. scovillei Miller as genotype.
- According to Cooper (1944, p.298) the genus possess undivided costae, actually too stringent a restriction and one not borne out by Cooper’s figures (1944 pl. 112, figs. 1,2). Wang’s illustrations (1949, pl.2, A,B) show that both A. kankakensis and A. whitfeldi have bifurcating and (or) intercalated costae. Foerste (1912, pl.8, fig. 8) shows that A.scovillei has few costae with almost no tendency to bifurcate or intercalate except close to the margin.
- Foerste (1912, p.131) differentiated A. scovillei from A. kankakensis and A. whitfieldi (which he believed synonymous) because it had approximately 40 rather than 60-70 costae. Winchell and Schuchert (1895, p.438) used precisely the same criterion to differentiate A. whitfieldi from A. kankakensis. But they placed equal weight on the supposed fact that he former had a much shorter hinge line than the latter. This interpretation is supported by Hall and Clarke (1892, pl. 5, figs. 24, 26) and their illustrations may have the same criterion to differentiate A. whitfieldi from A. kankakensis. But they placed equal weight on the supposed fact that the former had a much former hinge line than the latter. This interpretation may have been the basis for Winchell’s and Schuchert’s differentiation.
- Schuchert and Cooper (1932, pl. 9, figs. 16, 19) illustrated a specimen as A. whitfieldi that has the proportions and ribbing of A. kankakensis. Wang (1949, p.8, pl.2 A, B, figs. 1-5) illustrated the more transverse of two species as A. whitfeildi, but stated (p.9) that A. kankakensis has more numerous third generation costae. He expressed the opinion that outline is not diagnostic between the two species.
- The great variation in ribbing and in outline of the specimens from the Saturday Mountain formation suggests that neither of these can be relied on indiscriminately.
- Austinella is best characterized by its subquadrate outline, unequally biconvex profile, sub-rectangular ventral muscle field and Dinorthis-like cardinalia. Exteriorly, costae vary indefinitely both in shape and number. Winchell and Schuchert separated A. whitfieldifrom A. kankakensisupon the number of surface plications. They said: “… The plications are also numerous, there being from sixty to seventy along the margin of valve in that species ( A. kankakansis), while in Orthis whitfieldi there are usually not more than forty.”
- The writer examined many specimens labeled A. kankakansisA. whitfieldi and A. scovelli in the U.S. National Museum Collections (U.S.N.M. 24676, 39067, 48777, 87149). He noticed that most of the shells are marked by about 12-15 initial costae at the beak. Variation of number along the margin in mature shells is the result of a different scheme in later addition. In A. scovelli, the costae are flat and broad, usually simple, when increased, chiefly by bifurcation. On the other hand, A. whitfieldi and A. kankakensis always have subrounded costae with narrow interspaces, later additions taking place either by bifurcation or by intercalation. The writer believes that
and A. kankakensis can be distinguished only in their mature shells.