r>S(> PALEONTOLOGY OF ILLINOIS. 



indications of the usual minute surface granules appear to 

 be visible in some of the moulds left in the matrix. 



Length, about 1.20 inch; bight, 0.53 inch; convexity, 

 0.1 4 inch. 



This is ;i very n-:it, elegant species, of the type .1. clt'f/uns, Kinjjj nn d 

 .1. (ic!nH.:ii, Meek. It is a more slender species, however, \\ith much 

 more sharply elevated and more regularly disposed cost si- than the 

 former; while it \\ill also be readily distinguished, from the latter by its 

 costa-, and much more de])ressed umbones, wider (higher) posterior 

 extremety, etc. The regularity and prominence of its concentric costa-, 

 and their very abrupt termination a Ion }; the umbonal rid^e or carina, 

 are remarkable characters that ^ive the ])osterior half of the valves 

 much the appearance of some types of Trit/onin. 



I,ocnlihj <tn<l y>av///o Found by Mr. (! I;KKN, of the Illinois Survey, 

 in WJUTCII county, Illinois, in a black, bituminous limestone near the 

 base of the Coal Measures. 



ALLORISMA (<I:IMTZII, Meek. 



I'l. -Jti. l.'ij;. ti. 



Attnrisma eU-itit us, CfilMl/., l.-'Cli. Curl), mid I\V:I.H in Nrl... p. ):{ : Tab. I, li-. -Jl. (Not i.l'Kin^. (S-H.) 

 AU'n-ixiiHi (it'init;ii. Ml KK, I,^(i7. Am. ,l(iiu. Sci. anil Arts. Vol. 4J. n. s., )>. 17. 



<(nd locality Hoof shales of Coal No. 3; Knox county, Illi- 

 nois. 



(Jeuus (^JENOOAHDIA, M. and \Y. 

 CH^NOCARDIA OVATA, M. and W. 



PI. 27, Fig. 5. 

 Ch&rwcardia ovata. Mi i K and WOKTHBN. Proceed. Acad. Nat. Sci., I'liila., 18l!9, p. 170. 



SHELL obliquely ovate, more than two-thirds as >yide as 

 long, moderately gibbous, tlie greatest couyexity behitf a 

 little in front of the middle. Posterior outline rounding 

 into the cardinal margin above, and into the base \vith a 

 broad suh-semicircularcurye; deepest part of the base behind 

 the middle, from near which the anterior ventral margin 



