Streptograptus, Yin, 1937

Genus STREPTOGRAPTUS Yin, 1937 , emend. Loydell, 1990 and Maletz and Loydell 2021

Type species. Original specimen Graptolitus plumosus Baily (1871, pp. 22–23, fig. 1a-c.) is lost. Currently, neotype BELUM K12275a is figured by Loydell (1990) and came from the turriculatus Biozone of Tieveshilly, County Down, Northern Ireland.

Streptograptus pericoi Štorch, 1998a

Figures 8G View FIGURE 8 ; 9J View FIGURE 9

1998 “ Paradiversograptus ” aff. runcinatus (Lapworth) ; Gutiérrez-Marco and Štorch, p. 90, figs. 10 a, b, d.

1998a Streptograptus pericoi sp. n. Štorch; Štorch, p. 127, pl. II, fig. 6, text-fig. 3, fig. 4.

2015 Streptograptus pericoi Štorch ; Loydell, Frýda, and Gutiérrez-Marco, p. 771, figs. 17G, p. 779, 21AB, AL, AM.

2019 Streptograptus pericoi Štorch ; Loydell, Udchachon and Burrett, p. 372, fig. 8A.

Holotype. specimen no. MGM 3480 S, figured by Štorch (1998a, pl. II, fig. 6 and text-fig. 3, fig. 4), from the upper part of the linnaei Biozone ( hispanicus Subzone , early Telychian) of the Bádenas Formation at Checa section (Western Iberian Cordillera, Guadalajara Province, Spain).

Material. 8 incomplete specimens and fragments.

Description. The tubarium is gently ventrally curved and gently widening. Immature specimens are 19.7–20 mm long, exceptionally over 40 mm in one distal fragment. The most proximal part of the tubarium can be, in some cases, weakly dorsally recurved (here in three specimens out of eight). The sicula is 1.08 mm long, with an apertural width 0.17–0.22 mm. The sicular apex reaches to half level of th 1. Dorso–ventral width of the tubarium gradually increases from 0.25–0.4 mm at th 1, to 0.29–0.37 mm at th 2, 0.3 mm at th 3, 0.36–0.46 mm at th 5, 0.54 mm at th 10, and 0,72 at th 15. Mature specimens with more than 15 thecae attain a maximum distal width of 0.74–0.87 mm. The prothecae possess an inward-sloping ventral wall. Coiled metathecae of streptograptid form occupy approximately two-fifths of the DVW in proximal thecae and one-half of the DVW in distal thecae. Accordingly, a coiled metatheca takes up approx. one-half of the total thecal length in the distal part of the tubarium. Extended, inward-facing thecal apertures point towards the dorsal side of the tubarium. The 2TRD values are 1.69–1.75 mm at th 2, 1.71–1.81 at th 3, and 1.65–1.78 at th 5. The presumed interthecal septum is steeply inclined.

Remarks. Streptograptus pericoi was described by Štorch (1998a) from the Checa Section in Spain. Currently, its occurrence is also recorded from another locality in Spain (El Pintado) and from the Sepon Mine (central Laos), along with the present record in the Prague Synform ( Czechia). Loydell et al. (2019) considered Str. pericoi to be one of the typical (peri) Gondwanan graptolite species. The sicular apex reaches half the length of th 1 in some specimens described in this study. However, in the original description by Štorch (1998a), a sicula reaches the top of th 1. The 2TRD values are almost identical to those in the original description throughout the tubarium – the differences in 2TRD values fluctuate in the order of 0.1–0.2 mm which may be ascribed to intraspecific variability. The overall trend of 2TRD values and its slight decrease towards the distal part of the tubarium remained the same. Specimens are preserved as flattened silvery impressions in low relief, and, unfortunately, in most cases pyritized. The species has been recorded only in the uppermost, Z0 layer of the test pit, which corresponds to the hispanicus Subzone and observations by Štorch (1998a) or Loydell et al. (2015). At the same or similar level in which Str. pericoi is found, the following species have been recorded in the peri-Gondwanan sections: Paradiversograptus runcinatus (Lapworth, 1876) , Streptograptus plumosus (Baily, 1871) , Streptograptus pseudoruncinatus ( Bjerreskov, 1975) , Monograptus pseudobecki ( Bouček and Přibyl, 1943) , and Streptograptus picarrai (Loydell et al. 2015) . When compared to Paradiversograptus runcinatus (Lapworth, 1876) , the Str. pericoi differs in shape of thecae and lower values of 2TRD. Paradiversograptus runcinatus possesses simply hooked thecae and 2TRD values 1.8–2.2 mm at th2 as noted by Štorch (1998a). Streptograptus plumosus (Baily, 1871) has a tightly coiled tubarium with markedly dorsally recurved proximal end comprising 2–4 thecae, broader metathecae that occupy more than one-half of the tubarium width distally, and prothecae with conspicuous folds at their bases as noted by Loydell (1992). Streptograptus pseudoruncinatus ( Bjerreskov, 1975) differs from Str. pericoi by having more closely spaced thecae as noted by Loydell (1993). Monograptus pseudobecki ( Bouček and Přibyl, 1943) differs in having narrower, rather hooked than coiled thecae (like P. runcinatus ) and slightly narrower proximal tubarium part (1.88 mm compared to 1.75 mm), with higher 2TRD2.

Streptograptus picarrai Loydell et al., 2015 from El Pintado section, has a similar tubarium curvature to other species listed above, but it has a greater DVW: 0.45–0.6 mm at th2, 0.55–0.8 mm at th5, and 0.65–0.9 mm at th10.