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Journal of Paleontology 92(3):388–397
auricle (Bailey, 1983). Although similar in shape and develop- ment of auricles, Actinopteria can be differentiated from Leiopteria Hall, 1883, which is also common in the Hamilton fauna, in having both radial and commarginal ornament, whereas Leiopteria possesses only concentric commarginal ornamentation. Differences between Actinopteria and Cornel- lites Williams, 1908 can be found in the gibbous, highly inflated left valve (LV) and only slightly convex to flat RV (LaRocque, 1950). Cornellites develops strong radial ribs on the LV and lacks ornamentation on the RV. Cornellites is characterized by a pronounced anterior auricle, whereas Actinopteria develops a stronger procrescent growth vector (LaRocque, 1950). Leptodesma Hall, 1883 is set apart from Actinopteria by the lack of radial ornament on its shell disk. Limoptera’s radial ribs are more prominent and widely spaced than in Actinopteria, and Limoptera’s outline is broader, suborthocline, and larger on average (Johnston, 1993).
Actinopteria boydi (Conrad, 1842) Figure 2.1–2.6
1842 Avicula Bodyii Conrad, p. 237, pl. 12, fig. 4.
1883 Actinopteria boydi; Hall, pl. 19, figs. 2–24, 26–30, pl. 23, figs. 5, 6.
1883 Actinopteria delta Hall, pl. 23, fig. 3. 1883 Actinopteria epsilon Hall, pl. 23, figs. 4–6, 8. ?1883 Actinopteria zeta Hall, pl. 23, fig. 9.
1884 Actinopteria boydi; Hall, p. 113, pl. 19, figs. 2–24, 26–30, pl. 84, figs. 16, 17.
?1884 Actinopteria pusila Hall, p. 123, pl. 84, fig. 3. ?1884 Actinopteria iota Hall, p. 127, pl. 84, fig. 7. ?1884 Actinopteria eta Hall, p. 124, pl. 84, figs. 8–11. ?1884 Actinopteria theta Hall, p. 125, pl. 84, figs. 18, 19. ?1884 Actinopteria delta; Hall, pl. 121, pl. 23, fig. 3. 1884 Actinopteria epsilon; Hall, pl. 122, pl. 23, figs. 4–6, 8.
?1884 Actinopteria zeta; Hall, p. 123 pl. 23, fig. 9, pl. 84, figs. 1, 2.
1962a Actinopteria boydi; McAlester, p. 23, pl. 3, figs. 25, 26 [see for synonymy].
Lectotype.—McAlester (1962a, p. 28) designated Conrad’s original specimen (1842, pl. 12, fig. 4) as the lectotype. Unfor- tunately, as noted by McAlester (1962a) and subsequent inqui- ries by the authors, the whereabouts of this specimen is unknown.
Revised diagnosis.—Medium-sized to large Actinopteria; shape of shell disk varying from subcircular to narrow; procrescent growth vector present; angle between hinge line and posterior sulcus variable. Ornamentation consisting of densely packed, evenly spaced, fine radial costae and evenly spaced, incremental commarginal growth lines covering entire disk and both anterior and posterior auricles.
Occurrence.—The type material is from the Middle Devonian (Givetian), probably Skaneateles Formation, of Hamilton, Madison County, New York, U.S.A. Actinopteria boydi
has thus far been identified only from Middle and Upper Devonian of the Hamilton, Genesee, Sonya, and West Falls groups of northeastern North America. Our study includes only specimens from the Middle Devonian Hamilton Group of New York State.
Description.—Shell medium to large (maximum length=8cm); inequilateral; inequivalve left valve more convex than weakly inflated to flattened RV; umbo broadly convex, with beak slightly extending above dorsalmargin and subterminal; main disk oblique and weakly retrocrescent with tightly curved posterior margin and more gently curved ventral margin; posterior auricle broad with long straight dorsal margin, delimited from main disk by sulcus; posterior auricular sinus shallow in adults, butmore pronounced in juveniles; anterior auricle small, rounded, clearly delimited from main disk by narrow sulcus and byssal sinus; byssal notch absent. Ornamentation consisting of densely packed radial costae, extending nearly all the way from beak to valve margin and occurring on both anterior and posterior auricles; undulations present in commarginal growth lines in some specimens, and some composite molds of LV preserving reticulate surface sculpture. RV weakly concave, with flattened umbo, posterior auricle extended as in LV, anterior auricle smooth, rounded, with sharp byssal sinus; radial sculpture weak to absent later in ontogeny. Pallial line continuous, extending parallel to shell margin from posterior adductor impression to small anterior adductor scar situated just anterior of beak. Ligament internal, supported by two or three longitudinal grooves parallel to dorsal hinge margin. Dentition unknown.
Materials.—Skaneateles Formation: Pompey Road Cut: 8 LV, 6 RV; Rt. 5: 9 LV, 3 RV; Rt. 12 North (Linsley loc. 20): 5 LV; South Five Corners (Linsley loc. 22): 1 LV, 1RV; Dipleura locality (Linsley loc. 11): 3 LV; Nickel Middle (Linsley loc. 21): 5 LV; 4 Easement Road: 2 RV; Oran Gulf Quarry: 44 LV, 24 RV. Ludlowville Formation: Madison County: 1 LV; Livingston County: 1 LV; Cayuga Lake: 1 LV, 3 RV; Cascade Road Cut: 9 LV, 4 RV; Coon Hill: 1 RV; Little Beards Creek: 2 LV; Skaneateles Lake: 5 LV, 1 RV. MoscowFormation: Otsego County: 1 LV; Seneca Lake: 1 LV; Taughannock Lower Falls: 1 LV; Deep Run Gully: 3 LV, 1 RV; Long Hill Road: 1 RV; Kashong Creek: 1 LV, 2 RV; Soul Road: 4 LV; Cayuga Lake: 11 LV, 3 RV.
Remarks.—Structures of internal morphology, including denti- tion, ligament, and musculature, are for the most part unknown and must be inferred from closely related species. Because of the apparent stability within pterineid families and the close rela- tionship between Actinopteria boydi and A. decussata (see below), it is reasonable to assume that A. boydi has shell ultra- structure similar to that in A. decussata as described by Carter (1990) and Carter and Tevesz (1978) with a simple prismatic outer layer and nacreous inner layers. Likewise, the dentition of A. boydi could be cardinal teeth and 1–2 posterior lateral teeth extending nearly the length of the hinge margin (Johnston, 1993). Because the valve interiors of A. boydi are poorly known, recognition of this species relies mostly upon shape and ribbing characters.
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