Didymograptellus kremastus n. sp., a new name for the Chewtonian (mid-Floian,Lower Ordovician) graptolite D. protobifidus sensu Benson & Keble, 1935, non Elles, 1933

Vandenberg, A.H.M., December 2017. Didymograptellus kremastus n. sp., a new name for the Chewtonian (mid-Floian, Lower Ordovician) graptolite D. protobifidus sensu, non. Alcheringa 42, 259–268. ISSN 0311-5518.

The ‘tuning-fork’ didymograptid previously referred to as Didymograpt(ell)us protobifidus is common in Victoria where it is confined to the Chewtonian (mid-Floian). Biometric differences indicate that the mid-Floian form is not conspecific with the holotype of the Darriwilian Didymograptus protobifidus Elles, 1933 and the Floian form is thus renamed Didymograptellus kremastus n. sp. Study of the Valhallfonna Formation faunas on Spitsbergen indicated that the Floian form of D. ‘protobifidus’ differs from Didymograptellus bifidus (Hall) in both its morphology and stratigraphic distribution but a later study of the Cow Head Group on Newfoundland concluded that they are one species. My study, of more than 50 specimens of Didymograptellus from the Floian of Victoria, Australia, shows that the two are different and that similar differences exist in the Cow Head Group populations of Didymograptellus. The Chewtonian (Ch1) Didymograptellus protobifidus Biozone is renamed D. kremastus Biozone.

Alfons H.M. Vandenberg, lanceolatus@hotmail.vic.gov.au], avandenberg@museum.vic.gov.au] Museums Victoria, GPO Box 666, Melbourne 3001, Victoria, Australia.