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Journal of Paleontology 91(1):116–145
Materials.—10 specimens, at least six mature, but only a very few with a preserved ancora umbrella, plus three questionably assigned to this species.
Occurrence.—R. orbitus Subzone and L. convolutus Zone; Cape Manning, Rookery Creek, and an unknown locality, Cornwallis Island. 10 specimens identified as P. cf. decurtatus from Cape Manning and Rookery Creek. Found in the R. orbitus Subzone and L. convolutus Zone, and S. guerichi and S. turriculatus zones (lower Telychian) in Arctic Canada, Czech Republic, Germany, and south China.
Description.—Tubarium up to 9mm long, ovate in outline, widening at moderate rate to the level of fifth or sixth thecal pair, then distally decreasing in width. Width at first thecal pair 1.0–1.3mm, maximum width 2.8–4.0mm, but tapering some- what distally. 2TRD is 1.0–1.2 at the first thecal pair, 1.5–1.7 distally. Prosicula generally preserved, 0.35–0.5mm long, with longitudinal rods, some metasicular fusellae preserved. Virgella 0.5mm long. Ancora umbrella rarely preserved, 0.8–1.0mm diameter and moderately deep (approximately to level of prosicular aperture, see Fig. 9.5), with three to fourwhorls of spiral lists. Ventralwalls of thecae aremarked by amid-ventral list and six to seven pairs of relatively fine, zigzag lists near the aperture. Thecae with straight ventral walls inclined at 70–75o to axis of tubarium distally. Pleural lists present, inclined inward.
Reticulum meshes of relatively delicate lists forming moderately fine meshwork, meshes five- to six-sided, ranging from 0.1–0.3mm diameter. Ancora sleeve seams all facing outwards. Stomata round to ovate, 0.3–0.6mm, bounded by slightly elevated, delicate, collar-like structure; spacing varies somewhat on individual tubaria from 0.3 to 0.6mm.
Remarks.—Specimens of this species largely overlap in dimen- sions of width and thecal spacing with those of Pseudoretiolites perlatus. Pseudoretiolites decurtatus is distinguished from P. perlatus in having a finer reticulum on the ancora sleeve, as documented by Bouček and Münch (1944), as well as more strongly inclined thecae mesially and distally, and, in our specimens, in having more pairs of zigzag list near the thecal apertures. The specimens illustrated by Lenz and Melchin (1987b, fig. 3C, F, G), one of which is reillustrated herein (Fig. 9.3, 9.6), were initially identified as
P.cf. decurtatus. These specimens differ from typical specimens of Pseudoretiolites decurtatus only in possessing a coarser reticulum on the ancora sleeve, and are here questionably identified as Pseudoretiolites
decurtatus. These specimens also show traces of preservation of continuous membranes on the thecal walls, which were also documented in the type material of P. decurtatus by Bouček and Münch (1944).
Pseudoretiolites cf. tianbaensis (Ge, 1990) Figure 7.1–7.8
cf. 1990 Arachniograptus? tianbaensis Ge, p. 80, pl. 8, figs. 10, 19 pl. 10, figs. 2–4.
Materials.—17 specimens, three of which are mature, and one immature specimen preserved up to the level of the second thecal pair.
Occurrence.—L. convolutus, S. guerichi and S. turriculatus zones from Cape Manning and Snowblind Creek, Cornwallis Island, and Cape Sir John Franklin, Devon Island. Pseudoretiolities tianbaensis is found in the L. convolutus Zone of south China.
Description.—Tubarium triangular, widening continually and uniformly fromancora umbrella up to at least the eighth thecal pair (the longest specimens in collection). Widens from ~1.0mm across ancora umbrella to 2.5–3.0mm distally (extrapolated to 2.8–3.4mm when flattened). 2TRD is 1.8–1.9mm (10.5–10 in 10mm). Sicula not preserved. Ancora umbrella moderately deep, three to four whorls of spiral lists, merges smoothly with first thecal pair and ancora sleeve, without lateral orifices, but with small ventral orifices. Thecae with straight ventral walls, inclined ~45o to tubarium axis, distal ends of thecal floorswith four to five pairs of zigzag lists that often retain fusellar tissue. Underlying the thecal floor is a relatively robust and ventrally curved external ‘pseudolip’ (defined above; see Fig. 7.5, 7.7) that creates an orifice between it and the overlying thecal lip, resulting in the appearance of double thecal apertural lips. Internally, most of the thecal framework is missing, preserving only some mid-ventral lists and transverse rods. Entire lateral surfaces of tubarium with a robust meshwork reticulummade of polygonal, sturdymeshes that are of uniform size at any one level, but which slowly increase in size distally. Stomata ovate, spaced at ~1mm intervals, with slightly raised rims, ~0.58mm long and 0.38mm wide.
Remarks.—Specimens of this species differ from any of the associated Arctic species of Pseudoretiolites in several ways: a robust and relatively evenly distributed reticular meshwork; the smooth junction of the ancora umbrella and succeeding
Figure 11. Scanning electron microscopy images of Pseudoretiolites? sp.: (1) GSC137637, specimen showing complete prosicula and metasicula, base of broken mid-ventral list (arrow) section MCM96-9 1.6–1.7 below reference, R. orbitus Subzone; (2, 6) GSC137638, (2) broken prosicula with fine longitudinal rods, complete metasicula and proximal portion of theca 11, outside of which is remnant of ancora umbrella with five spiral whorls, (6) enlargement showing proximal part theca 1 and porus (arrow), section MCM88-8 11.5, upper D. triangulatus/D. pectinatus Subzone or lower R. orbitus Subzone; (3) GSC137639, stereopair of partial specimen with complete sicula, partial preservation of base of theca 1 and broken mid-ventral list of theca 1 (arrow), MCM96-9 1.6–1.7 below reference, R. orbitus Subzone; (4) GSC137640, enlargement showing distal part of metasicula with proximal part of theca 11 aperture, section MCM88-8 11.5, upper D. triangulatus/D. pectinatus Subzone or lower R. orbitus Subzone; (5) GSC137641, well preserved ancora umbrella with six spiral whorls, prosicula preserved, section section MCM88-8 11.5, upper D. triangulatus/D. pectinatus Subzone or lower R. orbitus Subzone; (7) GSC137642, stereopair with complete ancora umbrella and post-umbrella meshwork up to the level of about theca 11, complete sicula, base of mid-ventral list (a) and attachment of nema to connecting rod (b), MCM96-9 1.6–1.7 below reference, R. orbitus Subzone; (8) GSC137643, poorly preserved specimen with coarse and very irregular meshwork, only partially preserved ancora umbrella, and complete prosicula and metasicula, section MCM88-8 11.5, upper D. triangulatus/D. pectinatus Subzone or lower R. orbitus Subzone; (9, 10) GSC137644, (9) laterally flattened specimen showing zigzag thecal walls with preserved fusellar bandaging, and thickened mid-ventral list of distal-most preserved theca (arrow), (10) enlargement showing zigzag thecal ventral floors, lateral apertural rod (arrow), underlain by heavy cortical tissue, section MCM88-8 11.5, upper D. triangulatus/D. pectinatus Subzone or lower R. orbitus Subzone.
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