Permian Productinae and Stropralosiinae of W.A. 
35 
that the S. horrescens group should be distinguished as Aulosteges, a sub- 
genus of Stroplialosia. But why a sub-genus? Strophalosia is distinguished 
by non-dendritic muscle impressions, a smallish cardinal process, a perclined 
area of moderate height in the pedicle valve and well-developed dentition. 
"What features, therefore, have Aulosteges and Strophalosia in common that 
would induce us to consider one as a sub-division of the other? The posses- 
sion of a concavo-convex shell with an area on the pedicle valve and usually 
a spinose ornamentation is surely insufficient evidence for this grouping when 
so many points of difference are considered. 
Fredericks has a more positive reason for distinguishing between the 
two genera. He says (1931, p. 209) rhat both genera are characterised by 
the presence of an apical apparatus representing a reduced spondylium. 
The apical plates have become delthyrial ridges and the secondary septum a 
median ridge. These elements, Fredericks says, retain their connection at 
the apex of the umbo. He publishes no diagrams in support of this 
hypothesis, which rests, therefore, solely on his interpretation of these struc- 
tures — structures which would be preserved in only those specimens where 
no deformation of the umbo had occurred. The presence of such a structure 
would not do more than suggest a similar origin for both genera, a view 
which has not been disputed, and if other points of difference are present, 
would not preclude the maintenance of each as a separate genus. 
Subge7iera. — Two subgenera of Aulosteges have been proposed: 
Wyatkina Fredericks. 
Strophalosiina Licharew. 
These subgenera agree with Aulosteges in essentials, but differ in minor 
details. 
Wyatkina Fredericks (1931, p. 210 footnote) with subgenoholotype 
Aulosteges gigas Netschajew includes : — 
“Stropralosia-\\ke forms^ yet with primitive apical apparatus 
devoid of delthyrial ridges and euseptoid. Ornamentation consisting 
of thin spines. Muscle impressions of the ventral valve and structure 
of the dorsal valve as in Strophalosia.” (The Strophalosia of this 
paragraph refers to the Russian forms, i.e., Aulosteges.) 
Licharew suggests (1937, p. 128) that the delthyrial ridg'es are probably 
only x^resent when the deposition of shell substance has been excessive and 
these ridges would be the outward manifestation of teeth. This explanation 
seems quite plausible. As few Aulosteges possess either teeth or delthyrial 
ridges, Fredericks’s subgenus would include nearly all the members of the 
genus. Farther observations are necessary before any conclusion can be 
accepted with certainty. 
Strophalosiina Licharew (1935, p. 369) with subgenoholotvpe Aulosteges 
tibeticus Diener is distinguished from other members of Aulosteges by its 
geniculate ])ediele valve and peculiar ornamentation. Anterior to the genieu- 
latioii the surface of the shell is covered with radial i>li("ations w'hile on the 
visceral disc the plications are replaced by irregular concentric wrinkles 
and radially arranged pustules. 
Tliese subgenera, Wyatkina and Strophalosiina are closely related. 
Indeed, from a study of the literature they seem identical, since according 
to Hamlet, A. tibeticus = A. medlicottianus, while Renz says that A. gigas “ 
