Geniculograptus typicalis

• Rhabdosomes have a markedly narrow proximal part that widens relatively rapidly to the maximum width
• Nearly square thecae on each side of a rhabdosome
• Thecae have the characteristic angular bend in direction of growth
• Thecae have flanges that appear in profile view as spines

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Davis (1998):

• Nearly square thecae on each side of a rhabdosome. Primarily found in the Edenian.

Erdtmann and Moor (1973):

• Rhabdosome diplograptid, theca climacograptid, median septum absent with a slightly undulating virgula extending throughout interior of rhabdosome from the apex of prosicula into extrarhabdosomal nema. Sicula with distinct virgella formed by fusion of metasicular fusellae and two oppositely-located apertural (antivirgellar) spines. Budding of the 1^1 from the foramen positioned obversely near apex of metasicula. Initial portion of metasicula and then turns up toward its aperatural end. Th 1^2 originates laterally and obversely from the concave portion of the th 1^1, approximately at the same level as the metasicular aperture, then bends up and around the obverse side of the metasicula toward its aperture. All subsequent thecae originate from the infrarhabdosomal coenocoel (common canal), which is partitioned by interthecal septa. The interthecal septa originate from short stem-like internodia branching at regular distances off the virgula and broadening distally into spade-like dividers. The exposed portions of the ventral walls of thecae display slightly convex infragenicular contours. The infragenicular interthecal wall intersects with the supragenicular wall at a sharp angle where a distinctive subgenicualr flange extends beyond the rhabdosomal outline. The supragenicular thecal wall is slightly concave in appearance, but as a whole parallel with the axis of the rhabdosome. At thecal apertures, the fusellae appear to be condensed, forming thickened rim-like collars that fuse laterally with both the interthecal septum and the prothecal walls of the subsequent theca. Fusellar zigzag sutures are observed along the median of interthecal septa, supragenicular walls, and at irregular positions on the prothecal fusellae.
• The thecal spacing has been counted in two 5 mm intervals, one at the proximal end and one at the distal end of each rhabodosome. This method better reflects the astogenetic increase of the thecal length. Most measurements regarding thecal morphology were obtained at the theca located in the position of the greatest width of the rhabdosome (DMAT). This theca is not essentially identical with the most distal theca, although it often is the last available theca in the immature or broken specimens. Data on thecal overlap ratio, and length and width of thecae were omitted because of difficulty in arriving at accurate definition of the dimensions in these characters. Also, internal morphological features such as those pertaining to the sicula, virgula, and interthecal septa, infragenicular wall structures, and initial budding could not be included in the biometric analysis because all type specimens and the 100 selected specimens are all imbedded in their matrix with the internal characters unavailable for measurement. The internal structures were investigated in isolated fragments and complete specimens obtained from limestone lenses of the Patriot localities. All observed internal morphological features fully agree with the detailed analysis given by Bulman (1932).

Carlson and Berry (1969):

• The rhabdosomes are fragmentary. The longest of them is 15 mm. The rhabdosomes widen from 0.5 mm at the aperture of the first thecae Th 1^1 to 1.5-1.6 mm at 5 mm from that level to a maximum width of 2.5 mm which is attained to 8-10 mm from the aperture of Th 1^1. The rhabdosomes thus have a markedly narrow proximal part that widens relatively rapidly to the maximum width. After maximum width has been attained, the rhabdosomes are parallel-sided throughout the remainder of their extent. The thecae have the characteristic climacograptid curvature. They number 7.5-8 in the proximal 5 mm of the rhabdosome and 7-8 in 5 mm in medial and distal parts of the rhabdosome. All of the thecae have flanges that appear in profile view as spines that arise from the genicular angle of the thecae. These flanges are 0.2-0.3 mm in length and they are oriented normal to the supragenicular part of the ventral thecal wall. The thecae overlap approximately 3 times as long as they are wide in the distal part of the rhabdosome. The supragenicular part of the ventral thecal wall is 0.4-0.5 mm long. The apertural excavations of those thecae in the medial and distal parts of the rhabdosome are 0.3-0.4 mm in depth and 0.2-0.3 mm in height. The sicula is approximately 1 mm long. It has a virgella spine that is 0.8-1.0 mm long.

Ruedemann (1908):

• Synrhabdosome not observed. Rhabdosome long (66 mm +), narrow, with extremely narrow whip-shaped sicular end (.3-.4 mm) which in the space of about 16 mm attains the mature width (2-2.4 mm). The latter is maintained to the growing end. Lateral sides convex, smooth, broad. Sutural grooves so faint that they are observed only in exceptional cases. Sicula short (1.2 mm), its aperture possessing two short mucros. Thecae closely arranged (11-15 in 10 mm), overlapping one third in mature part, one fourth and less at sicular end; twice bent; in the proximal half parallel to axis of rhabdosome, then abruptly turning outward at nearly right angle and finally again becoming parallel to axis. Aperture horizontal to slightly everted (especially in neastic part) apertural excavation short (one fourth of ventral margin) and deep (on fourth of width of rhabdosome). Nemacaulus very thin and short and hence rarely observed.

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