28 
BULLETIN OF THE LABORATORIES 
and finely striated mesial fold. From S. striatiformis it also differs in 
the two first mentioned particulars. 
Shell of medium size, quite gibbous, triangular in outline, hinge 
equalling the extreme width ; anterior, margin angulated in the middle, 
forming with the hinge roughly an isosceles triangle of 45°; hinge ap- 
parently not, or but slightly, mucronate. Dorsal valve prominently 
convex along the longitudinal axis, rather strongly arched ; beak mod- 
erately prominent; fold triangular, rather high, sides of shell sloping 
rapidly from it toward the sides. Surface covered by nearly sixty 
small rounded, persistent striae, which rarely bifurcate near the front. 
From eight to ten striae fall upon the fold which in spite of its promi- 
nence (and because of the similar convexity of the valve) is poorly de- 
fined. Ventral valve very convex, provided with a deep, triangular, 
but narrow sinus and sculptured as the dorsal valve. Width of dorsal 
valve, 37 mm., height, 29 mm. 
All our specimens are casts of separate valves in the sandy parts 
of conglomerate I. There is reason to accept the suggestion made in 
the last volume that this species forms a link between the S. marionen- 
sis and S. striatiformis. 
ALLORISMA NOBILIS, Uekou. 
[See Bui. Den. Univ., Vol. iii, p. 71.] 
Additional specimens of this fine species enable us to add the fol- 
lowing facts : 
There is a considerable range of variation. The shortest speci- 
men seen measures 92 mm. in length, 25 mm. in height at the umbo. 
The beak is strongly incurved and is more produced than represented 
in Plate X, Fig. 5, of vol. iii. The effect of this is to make the anter- 
ior margin somewhat curved and less extended than there drawn. 
The surface is marked by very fine thread-like concentric striae as well 
as the coarser ones and also by the granular radiating striae characteris- 
tic of the genus, the later being rarely preserved. 
ALLORISMA CUYAHOGA, Sp. n. 
(Plate X, Fig. 34.) 
Shell of medium size, quadrately sub-elliptical, the length equal 
to twice the height, moderately convex; height nearly equal at both 
ends; posterior margin obliquely truncate^ as is the front; hinge mar- 
