142 
appears to me to have erred in considering as Devonian the specimens of this 
species which were sent him by Mr. Daintree, and which were found by that 
Explorer at Gympie, in Queensland, associated with several other Carboni- 
ferous species. 
Prodtjctus MAGNUS, Meek and Worilien, 
PI. X, Pig. 1. 
J^TOductuS niagnilS, Meek and Worthen, 1861, Procs. Acad. Nat. Sc. Philadelphia, p. 142. 
,, „ Idem, 1868, Geol. Survey Illinois, III, p. 528, pi. 20, fig. 7. 
This large and beautiful species is subhemispherical ; its hinge line 
equals or slightly surpasses the transverse diameter of the shell. The ears 
are nearly rectangular. The ventral valve, subsemi- elliptical in contour, is 
moderately arched, slightly gibbous, and furnished on the lower two-thirds 
of its length with a wide but not very deep ventral furrow. The beak is 
small, only slightly recurved and scarcely projecting at all over the hinge line. 
The dorsal valve is concave, but the greater part of the visceral region is all 
but flat, while its marginal part is abruptly curved nearly at a right angle 
for a part of its length equal to about one- quarter of the whole length of 
the valve. The test of both these valves is thin in comparison with their 
size. Their internal structure bears a great resemblance to that of P. semi- 
reticulatus, Martin, but the muscular impressions are not so well marked as 
in this last. The internal surface of the recurved part of the dorsal valve is 
covered with a large number of small punctures, like pin pricks, rather close 
together. The external surface of both valves is ornamented with numerous 
longitudinal ribs, rather thin, not very regular, and often bifurcating ; on the 
ventral valve these ribs are interrupted in their course by numerous small 
tubular spines slightly widened and thickened at their base. A row of 
similar but more pronounced spines is found along, and at a short distance 
from, the hinge line of this same ventral valve ; these spines correspond to 
the punctures of the dorsal valve. Some faint concentric lines of growth 
cross the longitudinal ribs, not always producing a reticulated design like 
that which so clearly distinguishes P. semireticulatus from most of its 
congeners. 
Dimensions , following dimensions were taken from a specimen 
from Illinois, sent to the Brussels Boyal Natural History Museum by Mr. 
Worthen: — length, seven centimetres; breadth, eight centimetres; total 
thickness, 3.75 centimetres. The only Australian specimen sent me was 4.5 
centimetres long, and 5.5 broad. 
