

LAMKM.lim.VVI.mx I'.; 



more prominent. ^'ivm- it a more erect appearance than any of the other specie* 

 referred to the genus. Nor can I Hnd that .1. orbimlaria ever has concentric undu- 

 ations. 



Formation and loro/ttir.-Mi.l.ll.- tUlena, Wolsbach's dam, near Spring Valley, Minnesota; al. in 



.! nullity. Illn. 



Mtut. Ktg. No. 8343. 



AMBONYCHIA AMYODAI.INA //.///. 



I-K XXXV. FI08. I MM! I 

 .tm/>unyc/ii<i umwl'i/i'iii HALL, 1847. Pal. N. Y., Tol. I, p. !&. 



None of the specimens seen by me preserve the surface characters well enough 

 to prove that this species was provided with radiating lines. Obscure traces of such 

 -tri.i are to be made out on one of the casts of the interior, but the evidence is not 

 sufficient for me to assert that they are what they seem. Still, it is highly probable 

 that radiating stria> will be found on perfect specimens, in which case the species 

 would stand very near A. Mlistriala, differing from it, so far as we can now see, 

 chiefly in its greater size, less incurved beaks, flatter anterior side and less angular 

 postero-canlinal margin. 



The anterior lobe is longer, more sunken and less sharply defined in this species 

 than in the others here referred to Ambonychia. 



Formation and locality. Middle Galena of Good hue county, Mlnn.-sota. The Now York typ,- <,f 

 the species Is credited to the Trenton limestone at Adams, Jefferson county. Hilling* al*o catalogue* 

 the species from the same horizon In Canada. 



Genus CLIONYCHIA. I'lrirh. 



Ambonitehia (part.) HALL, 1847. Pal. N. Y.. vol. I, p. 163. 



ClioHgehui, ULICICII, 1892. American GeoloKlst, vol. x. p. 97; CKcmyeMo, MII.I.KU, 1802. First Ap- 

 pendix, N. A. Geol. and Pal., p. 899. 



Shells equi valve, moderately convex, subalate posteriorly; beaks terminal, com- 

 IM i atively small, not very prominent and but little incurved. Cardinal line straight, 

 rather long, forming an angle of less than 90 with the anterior side. Surface marked 

 concentrically only. No byssal opening, the margins closing tightly all around. 

 Mus-'tilar impressions situated in the postero-cardinal third, large, bilobed, the 

 lower lobe much larger than the upper. Pallia! line simple, extending from the 

 posterior adductor to the rostral cavity. Hinge plate of moderate strength, without 

 cardinal or lateral teeth, excavated longitudinally for a linear ligament. Upper 

 part of anterior edge thickened, producing a more or less well-marked impression 

 in this part of casts of the interior. Anterior pedal muscle attached a short distance 

 behind the beaks. 



Type: Ambonychia lamtlloxa Hall. 



