264 
PALEONTOLOGY OF NEW YORK. 
Test thin, marked by numerous fine concentric striae, which at irregular 
intervals have been raised into imbricating lamellae, leaving strong varices 
on the cast. 
Interior unknown. 
A specimen has a length of 52 mm. and height 25 mm. 
This species is distinguished from M. Chemungensis by its straighter form, 
erect beaks, and convexity along the medial line. 
Formation and locality. In the Yellow sandstones, at Burlington, Iowa. 
Mytilarca fibristriata. 
PLATE XXXIII, FIGS. 6, 7 ; AND PLATE LXXXVn, FIG. 6. 
Mytilus fibnstriatus, White and Whitfield. Proc. Boston Soc. Nat. Hist., vol. viii, p. 296. Feb., 1862. 
“ TVhitfieldianus, Winchell. Proc. Acad. Nat. Sci., Phila., p. 413. Sept., 1862. 
“ “ “ “■ “ p. 11. 1863. 
Mytilarca fibristriata, (W. and W.), Hall. Prelim. Notice, Lam. Shells, etc., pt. 2, p. 24. 1869. 
“ fibristriata (W. and W.) ( fimbristriata, in error), Hall. Pal. N. Y., vol. v, pt. 1. Plates and 
Explanations: PI. 33, figs. 6, 7. Jan., 1883. 
Shell of medium size; body very elongate, narrow elliptical; length more 
than twice the height; byssal area convex and inflated ; ventral margin 
nearly straight for two-thirds the length, thence curving into the abruptly 
rounded posterior extremity ; dorsal margin very gently curved to the' 
extremity of the hinge-line. 
Valves equal, moderately convex in the posterior part, becoming gibbous 
in the middle and anterior. 
Hinge-line short, oblique. Beaks narrow, sub-erect. Umbonal region 
narrowly gibbous. 
Test thin, marked by fine, thread-like, undulating radii, which are 
more or less interrupted by the fine concentric striae. 
Interior unknown. 
A specimen has a length of 48 mm., and height 22 mm. 
This species is distinguished from M. occide.nta.lis by its lesser gibbosity; the 
convexity of the body is along the ventral side instead of the median line; 
and by the presence of undulating, filamentous radii. 
Formation and locality. In the Yellow sandstones at Burlington, Iowa. 
