710 CA MBRIA X BRA CHIOPODA— WALCOTT. vol. xix. 



which was subsequently closed, the pedicle then protruding between 

 the valves, 



Tlu' only interior of any specimen of the genus thus far discovered 

 that shows a trace of muscular scars or vascular markings is the inte- 

 rior of tlie dorsal valve of I. j)a)i)iuh(, from near Rome, Oeorgia. All 

 that is discernible in this is a slight depression in the cast of the 

 interior, about one-third the distance from the beak to the front. A 

 rather strong vascular trunk arches forward on each side of it. nearly 

 to the center of the valve. 



iStrafii/raphic <li,sfrihntio)i. — The genus ranges from the lowest known 

 Lower Cambrian horizon to the upper portion of the Middle Cambrian. 

 The species thus far referred to the genus are as follows: 



Lower Cambrian : 



Iphidca hcHa, Billiujj:s. 



labradoriea, killings. 



var. swiintonensis, Walcott. 



j)n)inHla, White. 



jyrospecfensis, Walcott. 

 Middle Cambrian: 



Iphtdea cnnistria, new s]»e(ies. 



alahamaerms, new si»ecie8. 



lo(j(nii, lu'w species. 



orvaieJla, Linnarsson. 



pamntla, White. 



2)eah'i, new species. 



pusilla, Linnarsson. 



sculptilis, Meek. 



stissingensis, D wight. 



siiperba, new species. 



Ornamentation of the surface. — One of the most noticeable characters 

 is the surface ornamentation. In the type /. bella it is formed of sim- 

 ple concentric stria' and lines of growth. This may be called type A 

 and to it may be referred : 



Iphidea bella Lower Cambrian. 



labradoriea Lower Cambrian. 



var. swatitonensls Lower Cambrian. 



2)rospecttnxis Lower Cambrian; 



ahibamaensiii Middle Cambrian. 



logani Middle Cambrian. 



pnsiUa Middle Cambrian. 



siiperba Mid<lle Cambrian. 



stisKintjenifis Middle Cambrian. 



i-renistria Middle Cambrian. 



peaJci Middle Cambrian. 



The second type (B) is represented by I. ftculjytiUs, in which the striae 

 are more crenulated than in J. crenistria, but not sulliciently so to give 

 a diamond-shaped interspace. 



Type C is a beautiful surface, formed by the union of the crenulated 

 striie so as to make a line network of raised, obliquely arranged lines 



