296 
J.A. Long, G.C. Young 
Figure 7 Portalodus bradshawae gen. et sp. nov.. A, D, labial and lingual views of SN96a; B, lingual view of SN 96b, C, 
labial view of SN 93a. All x4. Latex casts whitened with ammonium chloride. 
17 and 26). The figured specimen (Young 1982, 
plate 87, figure 2) was noted to differ somewhat in 
sculpture of the ridges from other spines assigned 
to Antarctilamna, and CPC 21192 has only 16 costae 
on one side, whereas other spines have a greater 
number. More material is needed to clarify 
whether these spines actually belong to Portalodus. 
Stratigraphic occurrence 
The type material comes from Portal Mountain;, 
but the species is also found at "Gorgon's Head" 
near Mt Hughes (top level). Cook Mountains; Mt 
Gudmonson (level 6, top horizon). Fault Bluff, 
Cook Mountains, ("fish hotel" B site); Mt Crean 
(site MC7, Young 1988), Lashly Ranges, section 
"LA" (second outcrop south of Mt Crean L2 
section); Mt Ritchie, horizon "M". All occurrences 
of Portalodus bradshawae gen. et sp. nov. come from 
above the Turinia antarctica biozones (first 
appearance within the portalenesis zone) and range 
right through to the top of the biostratigraphic 
zonation scheme (occurring with phyllolepids and 
Pambulaspis at Gorgon's Head). 
Aztecodus gen. nov. 
Aztecodus hannsenae sp. nov. 
Figures 8, 9. 
Mcmurdodus ? ct.featherensis Young 1982: text-figure 
3H, plate 88, figure 4 
tooth ... tentatively referred to Mcmurdodus', 
Turner and Young 1987: 236. 
Mcmurdodus ? ct. featherensis, Davis 1994: 61. 
Etymology 
After the Aztec Siltstone, which has produced all 
the known specimens, and for Dr. Fraka Harmsen, 
California State University at Fresno, 
sedimentologist on K221-A136 Expedition. 
Diagnosis 
Shark with diplodont teeth up to 2cm wide, with 
a low base which is broader than the height of the 
cusps. Second principal cusp of nearly equal size to 
approximately three-quarters the height of the 
largest cusp, and both cusps are widely separated 
by a cutting ridge bearing approximately 12 small 
crenulations. Cusps are smooth both lingually and 
labially with strongly compressed cross-sections, 
and well-developed cutting edges. Small accessory 
cusplets usually developed at mesial and marginal 
ends of tooth adjacent to main cusps. Base low and 
broad in labial view, with two transverse canals. 
Ventral surface of base subrectangular with gently 
convex margins all round, and approximately 2.5 
times as long as broad. 
Remarks 
This genus differs from Portalodus bradshawae 
gen. et sp. nov. because it is based on broad teeth 
with cusps widely separated by a crenulated 
cutting ridge, by the low height of the base, the 
presence of very small accessory cusplets, and the 
paired transverse canals penetrating the the base. 
It is also generally of smaller size, although the 
largest specimen (WAM 92.3.59, Figures 8H, 9C) in 
width approaches the maximum height of 
Portalodus gen. nov. The larger size, central 
crenulated cutting ridge, wide separation and 
