Character A: Anterior Bridge Strut - 0. Anterior bridge strut does not extend significantly onto pleural one. It curves posteriorly to run perpendicular to the rib gomphosis. 1. Anterior bridge strut extends postero-medially to contact the rib gomphosis at a point approximately half way to the thoracic vertebrae. No buttressing of the sutural surface present. 2.Anterior bridge strut extends postero-medially to cross the rib gomphosis at a point approximately half way to the thoracic vertebrae and continue some distance posteriorly to it. Heavy buttressing of the sutural surface present, increasing medially.

     Character B: Retrahens Capitus Collique Muscles - 0. Enlargement of the retrahens capitus collique muscles and subsequent rugosity on the ventral surface of the carapace. This rugosity running from a point adjacent to the first thoracic vertebrae to the fifth thoracic vertebrae. 1. No such enlargement of the retrahens capitus collique muscles and hence no rugosity is evident on the undersurface of the carapace.

     Character C: Longissimus Dorsi Muscles - 0. Longissimus dorsi are small with no enlargement of the rib heads and arches. 1. Longissimus dorsi anteriorly enlarged with the first three vertebrae possessing enlarged rib heads and arches to accommodate them. 2. Longissimus dorsi enlarged throughout their length with all vertebrae possessing some degree of enlarged rib heads and arches.

The C. expansa group can be diagnosed from the possession of enlarged retrahens capitus collique muscles which is evidenced in skeletal material by rugosities on the undersurface of the carapace. They are further diagnosed by the possession of a large anterior bridge strut that continues to further than half way to the thoracic vertebrae from its origins on the fourth peripheral. The longissimus dorsi muscles in this group are enlarged anteriorly only with expansion of the rib heads restricted to the first few vertebrae.

The C. longicollis group does not possess the enlarged retrahens capitus collique muscles or their associated features. With the exception of the C. novaeguineae complex this group has a rather small anterior bridge strut and there is no enlargement of the longissimus dorsi muscles except in C. oblonga (Perth population) where the longissimus dorsi are greatly enlarged throughout the length of the thoracic vertebrae.

The holotype specimen is identical to the specimen originally illustrated by Gray (1841), down to details of an apparently longitudinally split fifth vertebral scute and the slight variation of the sutural contacts between the abdominal and femoral scutes (ie the specimen currently labeled as the holotype is the same specimen originally described and figured by Gray).

Figure 2. Ventral view of the holotype of Chelodina oblonga, with the plastron removed. To the left of the thoracic vertebrae is a disarticulated section of the cervical spine. To the right the rugosity of the retrahens capitus collique muscle can be seen as a feint white "scar" parallel to the thoracic vertebrae.

The three characters described here can diagnose the carapaces of the two groups within Chelodina. It is apparent that the holotype of C. oblonga is not the same as the current concept of C. oblonga from Perth. It would appear that the holotype is in actuality a specimen of what is currently referred to as C. rugosa from the Northern Territory, and that it may possibly have originated in Port Essington. Further morphological evidence of the distinction between the C. oblonga holotype and the current concept of C. oblonga from Perth can be gleaned from the description of C. colliei (Gray, 1856a), the next available name for the Perth species. In this paper Gray states that C. colliei (I hereby designate: BMNH 1947.3.5.91 as lectotype) could be differentiated from C. oblonga by the highly revolute marginals possessed by the former. The holotype of C. oblonga does not possess this character at all and this would indicate that Gray (1856a) intended that these be two separate species.

Since the name Chelodina oblonga (based on the holotype) technically applies to the Northern Territory form of the long-neck turtle currently known as C. rugosa and since C. oblonga is the senior synonym of C. rugosa, the Principal of Priority of the International Code of Zoological Nomenclature (ICZN, 1999; Article 23) might require a name change for the northern form. In addition, it might also be necessary to resurrect the name Chelodina colliei Gray, 1856a, for the southwestern Australian species from Perth. However, such changes would have a major destabilizing effect on current prevailing usage of Australian chelid nomenclature.

The ICZN (1999;Article 23.9) allows for the preservation of of junior synonyms that have consistent usage. However, to apply this rule to the C. oblonga - C. rugosa synonymy one must petition the ICZN and demonstrate that (1) the junior name (C.rugosa) has in the past 50 years been utilized by at least 10 authors in 25 publications and (2) that the senior name (C.oblonga) has not been used since 1899. Since C. oblonga is still currently in use and has been for 159 years since 1841, this article does not apply here.

Figure 3. Ventral carapace surface of Chelodina siebenrocki (UC 0212). (a) anterior bridge strut; (b)attachment site rugosity of the retrehans capitus collique muscle.

The ICZN (1999;Article 75.6) also allows for the conservation of prevailing usage by designation of a neotype. This rule applies to a situation as descibed here, where the holotype of a species name under prevailing usage is discovered to actually represent a specimen of a different species. One must then petition the ICZN to use its plenary power to set aside the original holotype and designate a neotype for the species. In this case, that would require that a neotype of C. oblonga be designated from a collection of animals from Perth, thereby allowing current prevailing usage of both names (C.oblonga and C.rugosa) to continue, and to avoid resurrection of the name C. colliei which has not been used for over 100 years.

Alternatively, trying to maintain the species concept as originally described by Gray (1841, 1856a) but erroneously synonymised by Boulenger (1889), one can petition the ICZN to suppress the name Chelodina oblonga Gray, 1841, and to place this name on the list of unavailable names. If successful such a petition would establish Chelodina rugosa Ogilby, 1890, as the available name for the northern long-neck turtle and resurrect Chelodina colliei Gray, 1856a, as the name for the species from Perth.

Until such time as a petition to the ICZN can be resolved, the recommendations of the ICZN (1999;Article 82.1) demand that prevailing usage be maintained and hence the current name for the northern long-neck turtle remains C. rugosa and that for the Perth species remains C. oblonga.

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