JAN. 19, 1921 PRICE: shell regeneration in a brachiopod 35 



have become inverted by reason of the pathologic condition of the 

 mantle and that it reformed the shell by inward growth. 



By whatever means accomplished, a layer of new shell substance 

 was spread across the break, overlapping the edges of the old shell, 

 and was deposited in part upon its inner surface. 



While the regenerative growth appears to have been abnormal in 

 direction and in the pattern of the resulting sculpture, yet the costae 

 are normal in size and only slight irregularities in spacing were pro- 

 duced. 



5- Rate of regenerative shell growth. — The rate of shell replacement 

 was sufhciently rapid to complete the patching before the death of 

 the animal. 



6. Time of the injury. — It may properly be inquired whether the 

 supposed break in the shell occurred before or after the shell had 

 attained its present height. It seems possible that the break may 

 have taken place when the shell had grown only to the last undulation 

 of growth posterior to the present front margin, or to some point 

 between these two lines. The unbroken continuity of the costae of 

 the "patch" up to the present margin without the interpolation of 

 new costae anteriorly suggests that the shell did not grow appreciably 

 in length after the "patch" was completed. A slight anterior diver- 

 gence of the costae of the "patch" at the border of the present margin 

 may indicate a little forward growth. If such growth did occur, it 

 may have taken place while the regeneration was in progress. 



There appears to be no indication as to whether the injury was 

 sufficient to affect the rate of general shell growth as the shell is within 

 the limits of the common adult size for the species. 



Summary of conclusions. — The impression of a pedicle valve of 

 Derbya crassa from the Pottsville Series shows a lobate area upon the 

 interior surface in which the normal direction of costal divergence is 

 reversed. 



1 . The costae of this lobe are fasciculate, a feature foreign to the 

 species. The inwardly diverging costae overlap the normal costae 

 in places. Other minor details of abnormal ornamentation are noted. 



2. The abnormal lobe is not a portion of a foreign shell but was 

 regenerated by the animal following a break in the shell. The mantle 

 also was probably damaged. 



3. The origin of the injury to the shell is problematical. The en- 

 closing sediment was deposited in quiet waters. If the injury was 

 caused by an enemy of the brachiopod, the form of the "patch" gives 



