

' 



Tin- AmtottycUa /.',, / H ,-,/iVi Meek an.i \V, ,.-[... ,,f the Galena, teems to be the 

 earliest species of now know ... IVrhaps contemporaneous 



form. occu- Tin* in the Trenton ,,f K,nt,, i Tennessee, that i< marcel, 



guMuble. from the llud-on Uuor / 



which two only an- d,-cnbed (I rdrona and robuta, of MHIer) occur in th, 



Km-r uii.l fine, .mat. n>ck-. So far as known the genus became e ,.th th,. 



close of tin- l.o\\i-r Silurian. 



INTKKMKDIA Meek >lli<l \\'<lhen. 



. KIUB. B-W. 

 .''!, w<ttu MUCK and WMUTIIKN, 1868. (i I II., vol. Ill, p. 308. 



shell -.mall, rliomhir Milmxatf. the length and bight about as eleven in to fourteen; 

 jjil'lM.ns iii thouml.onal, anterior and central regions, compressed ami subulate postero- 

 .loyally. Hiii^e line a little shorter than the greatest antero-posterior diameter of 

 the valves ranging at an angle of about 90 with the anterior margin. Anterior side 

 trum-at'.l nearly vertically al.ove. below rounding backward into the base, the outline 

 arnninl the lower two-fifths of the shell forming nearly a regular semicircle. Poste- 

 rior maririn -traightened above or rounding regularly into the hinge line. Beak* 

 prominent, full, ohm-fly pointed, strongly incurved with a slight forward din-.-ti.m. 

 Internal <-a>t.> are somwhat excavated in the upper part of the front in tl 

 surrounding the small byssal openinj:. and between the latter and the points of the 

 leaks tin-re i> a -mall protuberance representing the filling of a little cavity at the 



mity of the hinge plate. Surface marked by rather fine radiating plication-. 

 the total number, as near as can be determined from casts, being between forty-five 

 and tifty. They are coarser on the ventral slope than on the posterior wing, always 

 -implr and increase in strength with the growth of the shell. On large casts the 



i- are not defined except at the free margins, the rest of the surface being smooth. 



Mu-cular -mi and pallial line unusually obscure, their positions and form not 

 certainly determined. 



This little ^I.ell i< a tru- / ! 'i" and i|uit<> ditl"rent from Ambon Hi- 



'i Hall, with which Meek and \Vorthen compare it. It is related to the follow- 

 luit a nearer ally is found in the / Irich, of the lower part of the 



'incinnati expo>ur>s. That species, of which anexcellent internal cast is figured on 

 page 479 (Kg. :!'. pi. \ <. less gibbous, more oblique and has smaller beaks, wi 

 the inux-iilar scars and pallial line are n-u.illy nn> 



i m I l.r:ility (ial-na lltnesUinc, MountCarn.il. 1 '-hk*h. 



Wykoff. Mint)' - 



31 ut. Itrg. No 



