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The Hyoid Apparatus (Text–Fig. 2)
In 1951, I recorded that certain differences in the hyoid skeleton appeared to have a specific basis, as follows:
| L. hochstetteri | L. archeyi |
|---|---|
| 1. Definite anterior process present. | 1. No definite process. Sometimes a slight expansion of the ceratohyal. |
| 2. A clearly defined alary process present. | 2. Alary process absent (Except in one case (Trewavas, 1933) in which a small and unexpanded process was recorded.). |
| 3. Ceratohyal relatively narrow | 3. Ceratohyal relatively wide. |
In 1954, a head of L. hamiltoni was sectioned. The hyoid, unfortunately, was extremely buckled and a good reconstruction was impracticable. It could be seen, however, that an anterior process was absent, an alary process of simple type was present, and that the ceratohyal was relatively wider than in L. hochstetteri. Unfortunately, through an oversight, the reverse condition with regard to alary and anterior processes was recorded-i.e. it was stated that an anterior process was present and an alary process was absent (E. M. Stephenson, 1955, 799).
Fortunately, further material of L. hamiltoni has since become available. Figure 2F illustrates the hyoid of an old male specimen of L. hamiltoni from Stephens. Is An anterior process is absent and a slightly expanded alary process is present. The condition of the latter is not nearly so definite as in L. hochstetteri (Fig. 2B). The hyoid cornu is of no greater relative width than in L. hochstetteri.
Figures 2C and 2D illustrate the hyoids of female specimens of L. hamiltoni from Maud Is. In C, a small but definite anterior process is present, but in D a process of this kind is completely lacking. In a third specimen (not illustrated), the ceratohyal is expanded in the region in question. All three specimens show a slight though variable degree of expansion to form what can be called an alary process, but again this does not approach the condition of the same process in L. hochstetteri.
The hyoids of two specimens of L. archeyi are also illustrated (Figs. 2A and 2E). Neither provides any indication of an anterior process, but A shows a slight expansion to form an alary process. In both, the hyoid cornu is relatively wider than in the specimens of L. hamiltoni examined, though in neither A nor E is the condition so apparent as in the specimen illustrated previously (E. M. Stephenson, 1951, Fig. 15B)
From the data provided above, an amended table can be drawn up as follows:
| L. hochstetteri | L. archeyi | L. hamiltoni |
|---|---|---|
| 1. A very clearly defined anterior process present. | 1. Anterior process absent Sometimes a slight expansion of the ceratohyal (Trewavas, 1933). | 1. Anterior process highly variable, embracing any of the following conditions: —. |
| (a) Completely absent. | ||
| (b) Represented by as light expansion of the ceratohyal | ||
| (c) Present and clearly defined, though small. | ||
| 2. Clearly defined alary process present. | 2. Alary process completely absent or slightly developed. | 2. Alary process recognisable but not developed to the extent found in L. hochstetteri. |
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Text–fig 2—Hyoid apparatus, ventral view A—L. archeyi Specimen MB Mt. Moehau Male B—L. hochstetteri Specimen WHC Warkworth Mature female C—L. hamiltoni Specimen LMI Maud Is. Mature female D—L. hamiltoni Specimen LM2 Maud Is. Young female E—L. archeyi Specimen TA Tokatea Mature female I—L. hamiltoni Specimen H2 Stephens Is Old male
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As far as the relative width of the ceratohyal is concerned, this is greater in L. archeyi than in L. hamiltoni If, in fact, L. archeyi is comparable to a juvenile stage of L. hamiltoni, this is to be expected. It is probable that the specimen of L. hamiltoni described previously (E. M. Stephenson, 1955) was younger than any of the members of the same species described in the present account.
From the data supplied above it is clear that the hyoids of L. archeyi and L. hamiltoni have a much closer resemblance to each other than either of them does to the hyoid of L. hochstetteri.
A parahyoid bone is normally present in all three species. Its absence has been recorded in one specimen of L. archeyi (Fig. 2E).
Ascaphus truei has an anterior process but lacks an alary process (de Villiers, 1934a, and personal observation)
Text–fig. 3.—Vertebral column. A—L. hamiltoni Specimen H2 Stephens Is Old male Ventral view. B—L. hochstetteri Specimen TH. Tokatea Mature male. Dorsal view of sacral region. C—L. hamiltoni. Specimen H2. Stephens Is. Old male. Dorsal view of sacral region. D—L. hochstetteri Specimen WHB. Warkworth. Very young female Ventral view. E—L. hochstetteri. Specimen WHB. Warkworth Very young female. Dorsal view of sacral region. F—L. hamiltoni Specimen H2. Stephens Is. Old male. Posterior view of sacral vertebra.