Petrocrania scabiosa

• Encrusting brachiopod
• Small circular shape looks like scabs
• Very small and smooth
• Underlying ornamentation sometimes visible
• Sometimes concentric growth lines present

• Cemented pedicle valve thin; conical brachial valve may bear concentric
  growth lines

Davis (1998):

• Inarticulate brachiopod. Thin oval shell

Gregg (1948):

• Hall (1870) found that the surface of the valve of the brachiopod Crania scabiosa (Hall) [Petrocrania scabiosa (Hall)] was sometimes obscured by the roughness of the substance to which it is attached and caused irregular growth by which it often assumed the features of the foreign body.The fossil brachiopod Petrocrania scabiosa (Hall) was also reported by Hall (1892) to have maintained the marks of the sutures between the segments of a crinoid to which it was attached

Foerste (1924):

• Forms small, irregularly circular elevations on the surface of Strophomendiae and other places of support. Surface convex, usually reproducing the character of ornamentation found on its support, though there is a tendency toward even convexity with concentric striation.
• Locality and Horizon. Clay cliffs, south of Little Current, and Vars; and Snake island. In the Waynesville. Described originally from Cincinnati; range Eden to Richmond. Known also in Indiana, Kentucky, Tennessee, and Wisconsin. Similar specimens occur in the Richmond at Stonington, Michigan.

Hall & Whitfield (1875):

• Under Crania scabiosa
• Shell small, less than medium size, discoid or but slightly elevated, sometimes prominently and irregularly convex; irregular in outline, with thickened margins. Apex of the dorsal valve eccentric, varying in position in different individuals. Surface of the valves usually marked by strongly lamellose lines of growth, which are sometimes obscured by the roughness of the substance upon which they have grown, giving its character and form to the shell by causing it to grow irregular, so as to assume the feature of the body itsself. Ventral valve thin, not preserving the muscular marking and other features of the interior in a condition for description. The shells of this species are mostly found adhering to the surface of other forms of brachiopods, and are by no means uncommon. They generally assume the surface features of the body to which they are attached to such an extent as to become almost unrecognizable when attached to coarsely marked surfaces, and are not unfrequently mistaken for adhering rock, and forcibly removed. When attached to shells having moderately sized plications, the upper valve of the Crania is found to conform in surface characters to that of the foreign body, the plications passing obliquely across the valve, and it is only when attached to comparatively smooth surfaces that the true features of the shell can be obtained.

Hall (1868):

• Under Crania scabiosa
• C. scabiosa often with a considerable degree of convexity and a smooth exterior, usually adheres to Strophomena alternata.

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