Fauna of the Morrow Group 
155 
Productus welleri n. sp. 
Plate IX, figures 10-11 a. 
Description. Shell of medium size, sub-hemispherical in 
shape, transversely sub-quadrate in outline, wider than long, 
hinge -line longer than greatest width of valves in front. Di- 
mensions of two pedicle valves, the type and one other, art : 
length from hinge-line to anterior margin, 14.7 mm. and 13.0 
mm. ; length from umbonal region to anterior margin, 16.9 
mm. and 16.0 mm. ; length of hinge-line, +24 mm. and +20 
mm. ; width of valve midway from hinge-line to anterior mar- 
gin, 20.3 mm. and 19.2 mm. ; convexity of valve, 10 mm. and 
9 mm. Dimensions of three brachial valves, the allotype and 
two others, are: length from hinge-line to anterior margin, 
15.5 mm., +20 mm., and 11.5 mm. ; length of hinge-line, 26 
mm., 37 mm., and 16 mm. ; width of valve midway from hinge- 
line to anterior margin, 23 mm., 34 mm., and 15 mm. ; con- 
vexity of valve, 5.5 mm., 10.0 mm., and 2.5 mm. 
Pedicle valve strongly and regularly convex longitudinally, 
somewhat flattened above the visceral region and on the venter, 
and with steep umbonal slopes and main flanks; beak full and 
strongly incurved beyond the hinge-line, umbonal angle about 
100° ; cardinal extremities produced, cardinal angle acute ; ears 
longitudinally convex, fairly well set apart from the cardinal 
slopes and main flanks by a sinus on either side of the vaulted 
visceral region; a faint, shallow mesial sinus commonly origi- 
nates in the umbonal region and crosses the venter to the 
anterior margin, is normally an inconspicuous feature of the 
shell, and in some cases is absent. Surface of valve marked 
by numerous close-set, but ordinarily quite faint, radiating 
costae which display a tendency to become obsolete in old age, 
crossed in the umbonal region by moderately strong concentric 
ribs which are deflected outward upon the ears; faint concen- 
tric lines of growth are present in all stages and in old age 
become conspicuous undulations; a single row of prominent 
bases of comparatively large, erect spines, commonly eight in 
number, crosses each ear from umbo to lateral margin and 
forms an angle of about 15° with the cardinal line, other and 
smaller spine bases irregularly scattered over the surface of 
the valve. 
