I \MKI.I. Ill; \\. MIA I \ I'M 



' ' 1 1 il ] 



l>e iin.ri' nearly related to . I ml". n/.-/i/.i than eitherof the genera nient miied Certain 

 it i- that I tin.l it mi, I-.- .lilli.-ult to point out the di-tiii^mshin^ features than I <li.l 

 in tho>e c:i>es. Tin- genera I appearance of the shells of the two genera (A mboHif 

 ami .\Htfilii,;ili,i) i~ MTV -unilai.l.otli in thomatterof form and in their Hurface mark- 

 ing. Tin- hiii- MTV much the same in the two genera, the Vine! diilerence 

 I'fin- that the area i- wider in . I //./,/, //. The greatest difference, however, soemH 

 to li.- in the anteni-cardmal region, where the margin of the hitter is thickened, 

 ''*" ' ' I"' interior to appear as broadly impressed in this region. 



AMKONYCIIIA r IATA Hull. 



l-I.ATi: XXXV. KIUH. 1 nncl I 

 Amlio*tchia pliinittriul,, MA 1. 1., I". I I: ] 9g\ I. Sur. Win., p. 32. 



Shell obliquely aeii minute-ovate or subrhomKoidal. ventricose, with the i*>int of 

 convexity near the center of the antero-cardinal half. I | .| .er half of anterior 

 -id> xiuiievvliat llattene.l. nearly straight, sloping liaek ward slightly, and more rapidly 

 below, into the basal margin, which, with the greater part of the interior edge, 

 forms a semicircle; postero -cardinal margin subangular, hinge line straight, one- 

 third or a little less shorter than the greatest length of the shell beneath. I teaks 

 prominent, strongly incurved; umbones full and rounded; posterior cardinal slope 

 concave. Surface marked by distinct, broad and shallow concentric undulations 

 ami tine radiating strue, of which about twelve occur in "> mm. at the margin of an 

 average example. These stri.i , which are flattened and separated by very narrow 

 interspaces, are cancellated by another set of even finer concentric lines. Test very 

 thin, hinge plate narrow, apparently with two cardinal teeth in each valve and no 

 lateral teeth. In good casts of the interior the antero-cardinal lol>e is sharply 

 defined. 



This rare and beautiful species is readily distinguished from /(. Mlixtriuta Hall, 

 and .1. o;7//>M/</j-/.s- Kmmons, sp., by its concentrically undulated surface. In thi- 

 feature it is like Clionyrhin un<l.it>i Kmmons, sp., but that form, aside from the fact 

 that it has the characters of Clionychin, is less ventricose, of somewhat different 

 shape and without radiating lines. For comparisons with /(. tiffinis t'lrich, see that 



'nation and iorafffy.-Knmi tho I ue llm^ton*" t Mineral Point and Delolt, WiMoa- 



-m .-i t Canm.n Falls. MlnnemU, and Lee cuunljr. Illinois. 



*** Rfff. No. 8327. 



