264 PALEONTOLOGY OF NEW YORK. 



Test thin, marked by numerous line concentric stria?, which at irregular 

 intervals have been raised into imbricating lamella'. Leaving strong varices 

 on the cast. 



Interior unknown. 



A specimen has a length of V2 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, IK.s 6, 7. am. PLATE I.XXXVII, FIG 6 



Mytilus fibrist riatus, White and Whitfield. Proc. Boston Sue. Nat. Hist., vol. viii, ).. i".iH. Feb., 1862. 

 •• Whitjhhliiiniis. WlHCHBLl. Prop. Acad. Nat. Sci.. Pbila.. p. 418. Sept., 1862. 



p. 11. 1863. 

 Mytttarca fibristriata, |W. and W.), Hall. Prelim. Notice, Lam. Shells, etc.,pt. 2. p. 24. 1S69. 



" fibristriata (W. and W.) (fimbristriata, in error), Hall. Pal. N. Y.. vol. v. pt. 1. Plates and 



Explanations: PI. S3, ti<rs. 6, 7. Jan., 18S3. 



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 stria?. 



Interior unknown. 



A specimen litis a length of IS mm., and height 22 mm. 



This species is distinguished from M. occidentalis 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. 



