Io8 SMITHSONIAN MISCELLANKOUS COLLKCTIOXS VOL. 53 



midway by a relatively large, open, triangular delthyrinni. Dorsal 

 valve convex, with an elevated, relatively narrow median fold that 

 does not extend back to the beak ; area short and divided by a 

 strong, open, triangular delthyrium. 



Surface marked by concentric strire and a few strong lines of 

 growth. The largest shell is represented by a dorsal valve that has 

 a length of 12 mm.; wadth, 14 mm. A ventral valve 7 mm. in 

 length has a width of 11 mm. 



Casts of the ventral valve show a spondylium supported on a sep- 

 tum that extended from the beak about one-third the distance to the 

 front margin. The spondylium of the dorsal valve rests directly 

 on the interior of the shell without trace of a supporting median 

 septum. 



Observations. — The young shells of this species are almost 

 evenly convex, the fold of the dorsal valve and the sinus of the 

 ventral valve of the adult shell not having developed. The charac- 

 teristic spondylium of each valve is shown in the youngest .shells 

 observed. The general term of SyniropJiia cainphcUi is 'nuch Uke 

 that of Synirophia rotundata (Walcott) [1905a, p. 293]. and some- 

 what like that of HiicncUa texana (Walcott) [1905a, p. 294]. It 

 differs from the former in having the spondylium of the dorsal valve 

 resting on the interior of the shell and not supported on a septum, 

 in this respect resembling the spondylium of H. texana. Some shells 

 have a somewhat transverse posterior margin like that of H. texana, 

 but the larger number have the broadly acuminate outline of S. 

 rotundata. The muscle scars of the dorsal valve, as far as known, 

 are similar to those of Hucnella abnormis (Walcott) [1905a, p. 

 289]. 



Formation and Locality. — Upper Cambrian: Knox chert. 

 Bunker Hill, Greenville quadrangle (U. S. G. S.), 6 miles (9.65 

 km.) northeast of Rogersville, Hawkins County, Tennessee. 



SYNTROPHIA ? UNXIA, new species 



Plate 10, Figure: 10 



This species is represented by a single specimen of the ventral 

 valve from wdiich the shell has been removed by weathering. The 

 cast of the spondylium shows it to have been of the same type as 

 that of the ventral valve of Syntrophia primordialis (Whitfield) 

 [1878, p. 51] and S. harahuensis (A. Winchell) [1864, p. 228], and 

 to have been attached to the interior of the valve without any inter- 

 vening septum. The elongate rounded form and scarcely percept- 



