16 
K. L. Prendergast, 
exists throughout the semiretieulate group. Dictyoclostus semireticulatus 
(Martin), for example, has semiretieulate ornamentation throughput its 
growth, and no change takes place in the curvature. 
The Irwin River specimens show the same range of variation as those 
from the type locality. 
Comparison with other species. — The specimens of this species have 
little in common with Productus (Dictyoclostus) semireticulatus Martin s. 
str. to which species they have been previously assigned. They ditfer in 
having the brachial valve geniculate, the rugae restricted to the visceral disc, 
the arrangement of the spines on the visceral disc and the division of the 
ears from the flanks. Briefly the only characteristic common to both species 
is the presence of semiretieulate ornamentation. 
The species has much in common with Upper Carboniferous and Permian 
forms of India and China. It probably occurs in Timor (Basleo) as Broili’s 
figures and specimens (1916 pi. cxvi figs. 14-16) show the same characteris- 
tics as the Australian species and Broili gives a reference to Etheridge (1903) 
in his synonymy. Of the Chinese specimens P. taiyuanfuensis Grabau as 
figured by Chao (1927 p. 30 pi. i fig. 10; pi. ii figs. 1-12; pi. viii fig. 16) from 
the Taiyuan Series is very close to 1). callytkarreivsis. The costation of the 
Chinese shells is much coarser (the costae vary from 0.5 to 1.3 mm. in width 
as compared with 0.3 to 0.5 mm.), the larger spines are more numerous and 
more closely spaced, particularly the I’ow along the inner edge of the ears 
where each spine touches its neighbour. 
Z>. callytharrensis is undoubtedly related to the P. sj^iralis-subcostatus 
group from the Salt Range. Freeh first suggested that the forms P. spiralis 
and P. indicus were possibly the younger and older specimens of the same 
species, and Broili supported this. More lately Cowper Reed (1931 p. 2) has 
suggested that the whole group, P. spiralis, indicus, vishnu, aratus and 
subcostatus are probably all members of one species group. The neax’est form 
of this group to P. callytharrensis is P. indicus, but the Western Australian 
specimens may be distinguished from that species by the tendency in the 
Indian species for the costae to converge towards, and disappear in, the 
sinus. Also the spiral arrangement of the costae on the ears cannot be seen 
in the Australian specimens. The costation is much coarser in P. indicus 
(7 costae in 10 mm., 10 mm. from the umbo). 
Dictyoclostus callytharrensis var. wadei va.r. nov. 
PI. II., figs. 2-4. 
Bolotype. — U.W.A. 20453, fernigiiious limestone, two miles east 10° south 
of Mount Nicholson, Kimberley Division; Nooneanbah Series. 
Topotypes. — U.W.A. , A.58, A. 59, A.65, same locality and horizon. 
Diagnosis. — Shell as in Dictyoclostus callytharrensis but -with approxi- 
mately hexagonal outline and arched umbonal region. Ears reflexed but not 
offset from flanks. Pedicle valve sinuate, with semireticulation on almost 
one-third of curvilinear length of valve, costae irregular, prominent and 
enlarged on trail, converging towards sinus. Brachial valve unknown. 
Description. — The holotype of this variety is a weathered and decor- 
ticated specimen. It is 63.7 mm. wide at the hinge-line and 54.5 mm. long. 
The semiretieulate ornament of the visceral disc is badly worn, but probably 
occupied about 34 mm. along the curvilinear length. The ears, though refiexed, 
are continuous with the anterior margin of the valve. The trail is ornamented 
