lOO SMITHSONIAN MISCKLLANEOUS COLLECTIONS VOL. 5.^ 



WIMANELLA SHELBYENSIS, new species 



Plate io, Figure 3 



All the specimens representing this species in the collection are 

 flattened in the shale to such an extent that very little of the original 

 convexity of the shell is left and only the impression of the shell 

 remains, as the shell substance has been entirely removed, probably 

 by solution. The general form of this species resembles very 

 closely that of Billingsella ? appalachia (Walcott) [1905, p. 231]. 

 The casts show a high cardinal area on the ventral valve with a broad 

 delthyrium, and on the dorsal valve a narrow cardinal area with a 

 broad, open delthyrium. 



The exterior surface is marked by fine concentric line-s and a few 

 stronger varices of growth. A small ventral valve has a length of 

 8 mm., with a width of 10 mm. A larger one has a length of 18 

 mm. ; width, 22 mm. A small dorsal valve has a length of 10 mm. ; 

 width, 13 mm.; and the largest dorsal valve in the collection has a 

 length of 19 mm. ; width, 25 mm. 



The specimens show no traces of vascular or muscular markings, 

 in this respect resembling Wimanella anomala (Walcott) [1905(7, p. 

 230] and Billingsella appalachia. 



This species appears to be the Lower Cambrian representative of 

 Wimanella anomala, differing from the latter in having rounded 

 cardinal angles instead of the acute projecting angles so character- 

 istic of W. anomala. Wimanella shelbyensis has the same general 

 form as B. appalachia, but dififers from it in having a smooth sur- 

 face and in the absence of all traces of radiating ribs. It more 

 nearly resembles Wim,anella simplex (see p. loi), but differs from 

 the latter in being more transverse, and the cast of the umbonal 

 cavity is relatively smaller. 



It is a curious fact that in all the species above mentioned there 

 is no trace of a Vascular marking or muscle scar. All the species 

 occur in argillaceous shale and none of them preserve the shell sub- 

 stance. The shells appear to have been macerated and removed by 

 solution, leaving only a cast of the compressed inner or outer sur- 

 face of the valve. 



The associated fossils are Obolns sniithi (see p. 62), Micromitra 

 (Paterina) major (Walcott) [1905a, p. 304] Micromitra (Paterma) 

 williardi (see p. 60) and numerous fragments of two or three spe- 

 cies of Olenellus. 



Formation and Locality. — Lower Cambrian: Montevallo shale, 

 4 miles (6.44 km.) south of Helena, Shelby County, Alabama. 



