16 
PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 
The genus (part of the group of the section Scabrae of the Trigonias) 
is lunate in outline with very concave dorsal margin and even more 
curved, convex, ventral margin. The anterior portion is very inflated. 
The costae run diagonally. Posterior costae are plain or papillate. 
Anterior costae are coarsely tuberculate, with a median group that are 
tuberculate only towards the ventral ends. 
Pisotrigonia is very similar to Pterotrigonia van Hoepen and 
Ptilotrigonia van Hoepen, in each of which, however, all costae are 
tuberculate. 
Species of the genus include P. ventricosa (Krauss) 6 which occurs in 
the Uitenhage beds of South Africa, in the “Trigonia smeei beds” of 
Tendaguru (East Africa) and the Oomia beds of Kachh. P. salebrosa, 
the genotype, is regarded by Rennie as a synonym of P. ventricosa , and 
I agree. The forms recorded by van Hoepen as salebrosa are from the 
Ndabana beds of Zululand. Trigonia subventricosa Stanton from 
Neocomian beds in South Patagonia probably is correctly placed in 
Pisotrigonia although the tubercles on the anterior costae are small. 
This species is recorded but not figured by Piroutet from New 
Caledonia (1917, p. 128). 
It is doubtful if any other described species rightly can be placed 
in Pisotrigonia. Most other forms that have been compared with the 
ventricosa group belong to Ptilotrigonia. 
Pisotrigonia sp. PL 1, figs. 2, 3. 
Several fragments of external moulds and several internal moulds 
are present of a species of Pisotrigonia. It has the typical form of the 
Scabrae (strongly lunate outline and very 
inflated anterior) and has also the character- 
istic ornament and wide smooth marginal 
carina of this genus. Two squeezes from 
external moulds are figured, the smaller of 
which shows the usual strong ventral curva- 
ture ; and both show T a sharp change from 
strongly tuberculate, oblique, anterior ribs to 
simple, sharp posterior ribs. Both have 
concentric growth striae that do not show well in the figures. 
Sufficient is shown in these fragments to indicate that the species 
is distinct from the three forms that have been described for the genus. 
It is most similar to P. kraussi. Both forms have five posterior ribs 
with an abrupt change to coarse anterior ribs that bear very strong 
clavate tubercles. A study of the growth lines on the several fragments 
of this species suggests that the changing shape of the individual, from 
youth to maturity, is not unlike that of P. kraussi. 
The available material is not sufficiently good to justify the intro- 
duction of a new specific name. 
6 The bibliographic references to these species are as follows: — P. ventricosa 
Krauss sp. 1842, p. 30, redescribed and figured by Kitchen from the Uitenhage beds 
(1908, p. 91, pi. Ill, fig. 1) and from the Oomia beds (1903, p. 104, pi. X, figs. 
4-8); P. kraussi Kitchin sp. 1908, p. 95, pi. Ill, fig. 2; P. salebrosa van Hoepen 
1929 B, p. 20, pi. V, figs. 1-6; P. subventricosa Stanton sp., 1901, p. 18, pi. IV, figs. 
19, 20. 
