Swisher et al.—Achatella Delo, 1935
Table 1. Character matrix used in the phylogenetic analysis (Fig. 2) Characters
73
12345678 910111213141516171819
Pterygometopus sclerops 00000000 0 0000000000 Ingriops trigonocephalus 01100000 0 0000010010 Achatella achates 11211111 1 1111021031 A. katharina A. clivosa
A. retardata A. (s.l.) schmidti
11211111 1 1111021131 11 ?11111 1 1000001021 11 ?11111 ? 10 ?00011 0 1
? A. truncatocaudata 11211111 1 1
0 0
0 0
0 ? 0010 ?
A. consobrina 11201111 1 1101001031 Details of characters and character states are given in Appendix 1.
11211111 1 1101101121 ?
? 0000021
field relatively flat near the axis, curves strongly downward near the lateral margin. Interpleural furrows faint, separating at least nine pairs of pleurae. Pleural furrows firmly impressed, oblique, and terminating short of pygidial margin; separate subequal anterior and posterior bands. Faint tubercle sculpture developed over entire pygidium except for furrows.
Remarks.—Ludvigsen and Chatterton (1982) considered Achatella katharina to be a junior synonym of A. achetes, but study of type and new material indicates that they are closely related (Fig. 2) but distinct species. Characters shared between A. achates and A. katharina include a relatively short (exsag.) eye extending from L3 to S2 or the anterior tip of L2, and dis- tinct tubercles on either side of the median embayment of the anterior glabellar margin. Achatella katharina differs in having a palpebral lobe that is farther away from the glabella (e.g., compare Fig. 8.4, 8.11 with Figs. 4.2, 4.6 and 5.4), and outward curvature of the lateral cephalic margin behind the intersection with the posterior branch of the facial suture. The latter feature is expressed on well-preserved, uncompacted cephala from both the Kimmswick Limestone (e.g., Figs. 8.1–8.7, 9.1–9.3) and the Viola Springs Formation (e.g., Fig. 10.4–10.8), and appears to be of biological rather than taphonomic significance. Achatella carleyi is also a distinct species, and is separated
from A. achates by possession of a larger eye that extends farther back on the cephalon (e.g., Fig. 6.1, 6.6, 6.10), and outward curvature of the lateral cephalic margin behind the posterior branch of the facial suture (e.g., Fig. 6.1, 6.6). S2 is noticeably shorter (tr.) on testate surfaces in A. carleyi and does not reach the glabellar margin (e.g., Fig. 6.1, 6.6). The pygidial margin is rounded posteriorly, rather than pointed (e.g., Fig. 7.3, 7.5). The sculpture comprises coarse, closely packed granules with scattered tubercles on the glabella (e.g., Fig. fig. 7.1). Achatella achates shares the glabellar tubercles, but these are set in background sculpture of very fine, barely perceptible granules
(e.g., Fig. 5.3). Achatella consobrina Tripp (1954, pl. 4, figs. 26–33) has eyes that extend back as far as S1, although they do not reach the axial furrow. The median embayment is well developed but tubercles are not developed at the lateral margins. The pygidium of A. consobrina has a relatively longer axis that terminates very close to the posterior margin. Several other species are characterized by larger eyes than A. achates and which reach the axial furrow anteriorly,
including A. clivosa Lespérance and Weissenberger (1998, fig. 4.1), A. retardata (Reed, 1914;Morris and Tripp, 1986, pl. 4,
fig. 2), and A. kuckersianus (Jaanusson and Ramsköld, 1993, pl. 5, fig. 3a–b). The latter species has shorter genal spines than A. achates,whereas A. schmidti (Warburg, 1925; Jaanusson and Ramsköld, 1993, pl. 5, fig. 4a) lacks genal spines entirely. Foerste (1910; see also Foerste, 1919) established a new
variety of A. carleyi, A. carleyi rogersensis, for material from the “Cynthiana Formation” (= Point Pleasant Member of the Lexington Formation of modern nomenclature; Osborne, 1968) at Rogers Gap, Scott County, Kentucky. The holotype cranidium (Foerste, 1919, pl. 19, fig. 18a) appears to have an evenly curved lateral cephalic margin and a relatively small eye. It differs from A. carleyi in these respects but resembles A. achates, to which it is assigned questionably. As revised here, A. achates is variable in several characters,
including expression of the large tubercle on the occipital ring, which is barely perceptible in some cranidia (e.g., Fig. 4.2). While faintly developed in some specimens (e.g., Fig. 4.6), all cranidia display a degree of bifurcation of the S1 furrow and a secondary forward inflation of L1 near the axial furrow. The development of the subtriangular pterygometopid cephalic muscle scar is variably expressed, as is the median embayment of the anterior glabellar margin. The latter feature is generally more weakly expressed than in A. katharina and A. consobrina, and more similar in appearance to the subtly developed embayment of A. carleyi. Sculpture across the glabella ranges from large, irregularly spaced globular tubercles set in a background of very fine granules (e.g., Fig. 4.1–4.3, 4.6, 4.7) to smaller, more uniformly sized and spaced tubercles (e.g., Figs. 3.1–3.4, 5.1–5.3).
Achatella carleyi (Meek, 1872) Figures 6–7
1872 Dalmanites carleyi Meek, p. 424. 1873 Dalmanites carleyi; Meek, p. 170, pl. 14, figs. 2a–d. 1919 Pterygometopus carleyi; Foerste, pl. 19. fig. 17. 1940 Achatella carleyi; Delo, p. 111, pl. 13, figs. 22–24.
Diagnosis.—S2 narrow (tr.), terminates short of glabellar margin. Weakly developed median embayment on anterior glabellar margin. Eye does not reach axial furrow; extends from S3 to S1; weakly conical in lateral view. Lateral cephalic margin curved outward behind intersection with posterior branch of suture. Pygidium with rounded posterior margin. External
? 01031 ?
A. kuckersianus 11100111 0 000010 ?022 A. carleyi
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