Permian Productinae and Strophalosiinae of W.A. 
19 
posterior third of shell, eostate on anterior two-thirds, no development of 
folds on trail. Slight convergence of costae in sinus. Ornamentation on ears 
partly reticulate, partly costate, costae showing spiral arrangements. Row of 
spines along hinge-line and along line of separation of ears and flanks. 
Brachial valve flatly concave with strong geniculation. Ornamentation 
reticulate on visceral disc, costate on trail. Ears deeply excavated, smooth 
or with concentric wrinkles only. No spines. Cardinal process short, trifld. 
Well developed adductor muscle impressions. Muscle and brachial impressions 
of typical productid pattern. 
Description. — Only pedicle valves are known from Western Australia. 
These have the following dimensions : — 
Description. 
1. 
2. 
3. 
Length of hinge-line 
88*2 
63-0-f 
Height 
45*6 
58-1 
48-9 
Curvilinear length 
134-0 
112-0 
99-4 
The shell is large, as shown by the table, and curved in a regular spiral, 
there being no pronounced change in the rate of curvature throughout the 
period of shell growth. The umbo, though incurved, is blunt and scarcely 
overhanging the hinge-line. The hinge-line is straight and long, and forms 
the maximum breadth of the shell, about one quarter of this width being 
occupied by the ears alone. These are prominent features of the shell, they 
are strongly reflexed with a triangular outline. Their surface makes an 
obtuse angle with that of the flanks. A median sinus arises near the umbo 
and becomes deeper towards the anterior margin. 
The ornamentation is reticulate on the posterior third of the shell, the 
rugae and costae being equally developed, thus giving an even pattern. On 
the trail the costae become more irregular, this irregularity being due to a 
change in disposition of the costae above and below the large spines which 
develop sporadically in this part of the shell. No grouping of the costae 
into fasciculi is seen in this species. A row of strong spines occurs along 
the hinge-line and along the flanks at the line of separation of the ears. 
The ornamentation of the ears is one of the characteristic features of the 
species. No new costae arise along the hinge-line after the shell ornamenta- 
tion has ceased to be reticulate and those already formed become more widely 
separated as the shell grows and, following the curvature of the valve, show a 
spiral arrangement when viewed from the side. 
Comparison with other species. — The spiral ornamentation of the ears 
is a distinctive character of this species, and differentiates it quite clearly 
from Dictyoclostus caUytharrensis. The visceral cavity is much shalloww in 
the latter species, not showdng the arching in the umbonal region which is 
seen both in D. spiralis and in D. callytharrensis var. wadei. In both 
D. callytharrensis and its variation the costae on the trail are grouped into 
fasciculi, a condition not seen in D. spiralis. 
For the distinction of D. spiralis from the Indian members of the 
spiralis-suhcostatus reference should be made to Waagen (1884). 
