TIO SMITHSONIAN MISCEl/I^ANIiOUS COLLECTIONS VOL.53 



The dorsal valve is described as follows : 



"Rotundato-quadrate, the cardinal margin as long as the width 

 of the valve, the surface convex, except on the dorsolateral alations, 

 where it appears to be flattened. There is a central, acute, or 

 pinched-up fold, produced forward, and expanding as it advances. 

 There are indications of the existence of strong, distinct, subradiat- 

 ing costse. 



"Whether or not this is the brachial valve of the species repre- 

 sented by the preceding form, it is, at present, impossible to say ; 

 the two occur in the same bed, however." 



From the study of the various forms of Huenella described herein, 

 I think that the two valves belong to one species, and I take pleasure 

 in naming it after Dr. R. Etheridge, Jr. 



Formation and Locality. — Middle (?) Cambrian: Archaeocya- 

 thinas white limestone, near Wirrialpa, in the Flinders Range, South 

 Australia. 



HUENELLA LESLEYI, new species 



Plate 10, Figures 12 and 12a 



Only the exterior of the valves of this species is known. In form 

 and outline it is most nearly related to Huenella texana. It dif- 

 fers from the latter in being broader in proportion to its length and 

 in having narrow, radiating, rounded ribs over the entire surface. 



This is probably the oldest known Huenella. Billingsella colo- 

 radoensis (Shumard) [i860, p. 627] and Lmgulella manticula 

 (White) [1874, p. 9] occur in the same bed of limestone. 



The specific name is given in honor of the late Dr. J- P- Lesley, 

 State geologist of Pennsylvania. 



Formation and Locality. — Upper Cambrian: About 200 feet 

 (61 m.) above the Middle Cambrian and 1,025 feet (312.4 m.) 

 below the top of the Upper Cambrian, in the limestones of the St. 

 Charles formation, about 7 miles (11.27 km.) above the mouth of 

 Blacksmith Fork Canyon and 14 miles (22.54 km.) east of Hyrum, 

 Cache County, Utah. 



CLARKELLA, new genus 



General form rotund, unequally biconvex. Surface smooth or 

 marked by concentric striae and lines of/ growth. Ventral valve 

 convex at the umbo and with a strong, broad median sinus ; area 

 low and divided by a relatively large delthyrium. Dorsal valve 

 convex at the umbo, which is extended forward into a strong, broad 

 median fold. Cross sections of the valves near the apex and be- 

 neath the umbo show a spondylium supported by four or more septa 

 that divide the umbonal cavity into five chambers. 



