Spinograptus quadratus ( Lenz, 1993 )

Kozłowska-Dawidziuk, Anna, 2002, Agastograptus, a synonym of Plectograptus (Retiolitidae, Graptolithina), Acta Palaeontologica Polonica 47 (3), pp. 459-467 : 464

Spinograptus quadratus ( Lenz, 1993)

Agastograptus quadratus n. sp.; Lenz 1993: 16, pl. 5: 1–10.

Emended diagnosis.—Apertural processes relatively short, simple and broad, close to mid−ventral list. Mid−ventral list well developed, straight. Minimal reticulum. Ancora sleeve with distinct zigzag. Plectograptus −like thecal profile.

Discussion.— S. quadratus is similar to S. latespinosus in thecal shape, and size of rhabdosome, although the lateral wall in S. quadratus is wider proximally, and narrower distally. The difference is in a shape of apertural processes and lack of reticulum in the ventral walls. The mid−ventral list in S. quadratus is well developed in every theca, whereas in other species of Spinograptus that list is usually well developed only in proximal thecae ( S. lawsoni , S. reticulolawsoni , S. latespinosus ) or not developed ( S. clathrospinosus , S. spinosus , S. munchi ).

Material and occurrence.— S. quadratus is known only from Arctic Canada, Cape Sir John Franklin, Devon Island, Lobograptus progenitor Biozone.