Glyptograptus sp. A

Glyptograptus sp. A

Figures 8E View FIGURE 8 ; 9G View FIGURE 9

Material. 15 specimens

Description. The tubarium is relatively narrow, usually only 4–5 mm long, with one exception reaching 11 mm. The proximal end is pointed. Most of the sicula is covered, the ventral wall is exposed by approximately 0.3 mm. The sicular aperture is approx. 0.2 mm in width. No virgella is preserved. The tubarium width increases slightly, but constantly from 0.7–0.8 mm at first thecal pair, through 1 mm at th3, to 1.1–1.2 mm at th10. Thecae inclined at 25–32° to the tubarium axis exhibit gently convex supragenicular walls. Concave thecal apertures are 0.27–0.3 mm wide, slightly everted and nearly perpendicular to the thecal axis. The length of th 11 is 0.6 mm, the length of th 12 varies between 0.7–0.8 mm. Thecal excavations are shallow in the proximal thecae. Thecae overlap for about one-half of their length. The 2TRD is 1.2–1.3 mm at th2 and about 1.3 mm at th5. The medium septum and nema were not recorded.

Remarks. All specimens of Glyptograptus sp. A were found in samples Z1 and Z2. Tubaria always were relatively narrow and short. Only one specimen attained the length of 11 mm. From the overall morphology and measured parameters, it appears that all specimens belong to the rich Glyptograptus tamariscus group. According to detailed descriptions and illustrations provided by Loydell (1992), the studied specimens resemble Glyptograptus elegans by Packham (1962) in tubarium width and 2TRD values. However, due to the large proportion of immature specimens in the present material, definite species assignment is not possible, and the species is left in open nomenclature. Commonly used 2TRD values have a limited value in juvenile specimens (e.g., in a specimen having 5–6 thecal pairs – the last pair does not reach full maturity and, therefore, does not allow for 2TRD5 measurement.