298 



PALEONTOLOGY OF NEW YORK. 



in Centronella. The adult condition of the loop is derived from this primitive 

 condition by progressive resorption of the pointed anterior portion of the plate, 

 and the complete obscuration of the median suture by anchylosis is not effected 



FIG. 216. Fig. 217. Flu. 'ilS. 



Dielasma turgula, Hall. 

 Fig. -JKi. The ceulrouelliloriu stage ol' the loop. X li. 



Fig. 217. A later stage; showing the resorption of the anterior portion of the loop. X G. 

 Fig, 218. Early Dielas.ma stage, produced hy further resorption. X 6. 

 Fig. 219. Loop and hinge-plate of a mature specimen. X G. 



FIG. 219. 



till near maturity. It is thus clearly demonstrated that the brachidiuni of 

 DiELASMA and, inferentially, all similarly recurved loops are secondary modifica- 

 tions of the primitive structure linding its mature expression in Renssel^eria 

 and Centronella. 



DIELASMINA, Waagen. 1882. 



1882. Dielasmhia, VVaaljen. Pi'oiiuctiis-liineatone Fossils ; Brachiopoda, p. 369, pi. xxvii, tig. 10. 



This name has been applied to certain plicated species in the Productus- 

 limestone of India, which possess more or less of the characters of Dielasma. 



FIO. 220. 



FIG 221. 



Dielasmina plicata, Waagen. 

 Dorsal and frontal views. 



IWaagen.) 



They have the dental plates of the pedicle-valve and tlie general form of the 

 brachidium in that genus, as for as the interior is now known, but for the 



