252 
As compared with Prodwctus scabriculus, the present one is much more genicnlate, 
hut they frequently otherwise resemble one another in shajje. Our species does not 
jjossess a divided septum in the dorsal valve ; hut, on the other hand, an area is present, 
the surface of the dorsal valve is far more concave, and the spine bases on the surface 
of the ventral valve quite lack the regular and close arrangement of those of P. 
scahriouhts. 
As a rule, when examined in the state of casts, the muscular scars of P. 
Irachythcervs do not appear to he highly developed, and, as compared with similar 
features in P. subquadrntus, there is a marked difference. But in examples of the former 
from the Darr Kiver,* in which the whole of the shelly matter is practically retained, 
this difference is not of so marked a character, and it is further evident both that the 
shell attained a very considerable thickness, and that a distinct area was present (PI. 
44, flg. 14'). This varies much in breadth, sometimes becoming quite linear, and at 
other times broad and appreciable. 
Loc. and Horizon. Stonehuinpy Creek, and Pelican Creek, near No. 1 Bore 
{R. L. Jack) — Middle or Marine Series, Bowen Bivcr Coal Pield ; Havilah-Byerwin 
Eoad, one mile south of Hosella Creek-crossing (2E. L. Jack) — Marine band in the 
Upper or Preshwater Series, Bowen River Coal Rield, associated with Perhyia senilis ; 
Penestella Hill, Encriuite Creek, and Stony Creek, Stanwell, near Rockhampton {The 
late James Smith) ; Limestone, close to Tarrol Station, Burnett (IFi H, Rands) ; Spring 
Creek, Cania, Burnett (TF. H. Rands) — Gympie Beds; Darr River f (Prof. A. 
Liversidge) ; Richards’ Homestead, three miles south-west of Mount Britton Town- 
ship (A. Ij. JAorisset) — Middle or Marine Series, Bowen River Coal Held. 
PnonuCTUS sttequadbatus, Morris, PI. 38, figs. 7-10 ; PI. 40, fig. 5. 
Productiis suhquadratuSt Morris in Strzelecki’s Phys. Desc. N. S. Wale.s, &c., 1845, p. 284, 
„ De Koninck, Mon. Gen. Productus, p. 203, t. 14, f. la and 6. 
,, He Koninck, Mon. Productus et Chonetes, 1847, p. iOO, t. 14, f. la and h. 
,, Ktheridge fil., Proc. K. Phys. Soc. Edinb., 1880, v., p. 283. 
Sp. Ohar. Shell largo, quadrate-triangular, inflated, gibbous, and very geniculate, 
being produced much towards the front ; when viewed laterally the sides are wall-like, 
but when seen from the dorsal side the shell has a more expanded appearance. Ventral 
valve very convex and much curved, inflated about the middle of the shell ; a well" 
marked sinus usually extends from the umbonal region continuously to the front margin, 
shallowing towards the latter, and giving to the valve a more or less bilobed appear- 
ance ; sides vertical, and flattened ; umbo large, thick, incurved, but not overhanging 
the hinge-line, or produced beyond it ; area short and triangular, transversely striate ; 
pseudo-deltidial aperture triangular and very marked, the area on each side below it 
sometimes thickened into a blunt prominence (hardly teeth) ; adductor scars deeply 
impressed, forming prominent oblong or oval eminences in casts, vertically ridged and 
grooved, cardinal scars narrow, elongate and deep, the median dividing groove very 
linear ; umbonal cavity much pitted and grooved. Dorsal valve flattened above, 
becoming concave and geniculate tow'ards the front, when the valve often becomes bent 
almost in the form of a right angle ; hinge-line rather shorter than the width of the 
valve, with the alar angles rounded ; area longer and narrower than in the ventra 
valve; septum entire, strong, sharp, extending to within a short distance of the front 
edge, and distally projecting as a thick and strong cardinal process far into the 
umbonal cavity ; alar ridges inconspicuous; adductor impressions in deep depressions, 
* There must be some mistake as to the locality of this example, as the Darr Eiver is wholly in the 
Kolling Downs Beds. Perhaps the “Don,” near Rockhampton, is the river referred to. (R.L.J.) 
t Locality doubtful. (B.L.J.) 
