220 PALEONTOLOGY OP KENTUCKY. 



Modiomorpha mytiloides. CONRAD. 



CypricarditiS mytiloides, Conrad. Geol. Surv. M. Y., Ann. Rep. 1841. 



Modiomorpha complanata, Hall. In err. Pal. N. Y., Vol. 5, pi. 1, plates and explanations, pi. 38, figures 



1-161883. 



Modiomorpha planulala, Hall. Prelim. Notice Lamellib. 2, p. 74 1870. 

 Modiomorpha mytiloides, Hall. Pal. N. Y., Vol. 5, pt. 1, p. 2771885. 



Shell larger than medium size, rhomboid- ovate, oblique ; length less than 

 twice the height ; basal margin nearly straight, or very slightly concave ante- 

 rior to the middle, curving to anterior and posterior extremities; posterior 

 margin abruptly curving below, and more gently recurving toward cardinal 

 line ; cardinal margin arcuate. Anterior end narrow, extended, abruptly 

 curved on the margin ; somewhat defined by the sinus, which extends from 

 anterior of the beak to the middle of the shell. 



Valves moderately convex, in old shells gibbous in the umbonal region. 

 Hinge-line oblique, extending to about the middle of length of shell. 



Beaks appressed, situated a little more than one-fourth the length of shell 

 from anterior end. Umbonal region not defined; convex in young specimens, 

 becoming more gibbous in older ones. 



Test of moderate thickness, concentrically striated with irregular lines of 

 growth, which are sometimes elevated into concentric ridges. The post-cardi- 

 nal slope in well-preserved specimens shows fine vascular markings. The an- 

 terior muscular impression is well marked, and situated just within anterior 

 margin below beak. Other interior characters are not known. 



An average sized individual of this species has the following dimensions : 

 length, twenty-six lines ; width, seventeen lines, and thickness, ten lines. 



This species resembles somewhat in form Mod. concentrica, but its anterior 

 end is more produced, and it does not show the concentric striae of that 

 species. It also resembles some forms of Mod. alta, but is more elongate, and 

 possesses a more regularly rounded posterior extremity, and a narrower an- 

 terior end. 



Formation and Locality. Occurs in the chert of the Devonian formation in Jefferson county, Ky., 

 and in Clark county, Ind., in company with its congeners, Mod. concentrica, alta and affinis. Watson's 

 Station, in Clark county, Ind., on the Ohio and Mississippi Railroad, furnishes fair specimens in a silicified 

 condition. 



Genus Nucula. 



Lamarck. 



Nucula, Lamarck. Hist. Nat. Des. An. Sans Vert. 1815. 

 Etymology: nucula, a little nut. 



Shell small, equivalve, inequilateral, trigonal or transversely elliptical or 

 sub-circular. Anterior or posterior extremity sometimes produced, usually 



