Fauna of the Morrow Group 
183 
?1910. Spirifer rocky montanus. Raymond, Ann. Carnegie Mus., vol. 7, p. 
156, pi. 24, fig. 5. 
Vanport limestone: New Castle, Pennsylvania. 
?1911. Spirifer rockymontanus, Raymond, Penn. Topog. and Geol. Surv. 
Comm., Rep. for 1908-10, pi. 3, fig. 5. 
Vanport limestone: New Castle, Pennsylvania. 
?1911. Spirifer rockymontanus. Mark, Bull. Sci. Lab. Den. Univ., vol. 16, 
p. 308, pi. 8 , fig. 10. 
Mercer limestone: Somerset, Ohio. 
Description, Shell of medium size, about three-fourths as long 
as wide, somewhat variable in outline, hinge-line less than, equal 
to, or greater than maximum width anterior to cardinal region, 
both valves strongly convex. Dimensions of four individuals 
of varying sizes are: 
Length from hinge-line to 
anterior margin 
-+-15 
mm., 
11.6 mm.. 
6.0 mm., 
3.8 
mm. 
Distance from umbonal region 
of pedicle valve to 
anterior 
margin of mesial sinus “'“19.5 
mm., 
14.2 mm.. 
7.1 mm., 
4.4 
mm. 
Length of hinge-line 
28.8 
mm., 
“^15 mm., 
7.7 mm., 
4.3 
mm. 
Greatest width of shell... 
along hinge-line 
, 17.9 mm.. 
9.0mm., 
4.9 
mm. 
Maximum thickness of 
shell “I“12 
mm.. 
10.1 mm.. 
5.0 mm.. 
3.0 
mm. 
Number of plications in sinus at 
Anterior margin 9 7 3 1 
Number of plications on fold at 
anterior margin unknown 8 4,2 
Number of plications on either 
side of fold and sinus at anter- 
ior margin 11 or 12; 9 or 10; 6, 7, or 8; 4 or 5 
Pedicle valve strongly convex, the longitudinal curvature 
greater than the transverse, the beak strongly elevated, some- 
what narrow and incurved high above hinge-line; cardinal area 
triangular, concave and transversely striated, delthyrium higher 
than wide; mesial sinus well-defined, originating on the umbo 
as a simple depression between two strong plications, enlarging 
and deepening toward the anterior margin, its plications arising 
by dichotomous division from those which bound the sinus as 
well as by bifurcation, the number of plications in the sinus 
depending upon the size of the shell but in the majority of cases 
being 7 or 9 ; lateral plications like those in the sinus, subangular 
and strong, usually from 9 to 12 occurring on either side of the 
