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 



no. 216. FlO. 217. Flu. 218. 



DieUuma turgida. Ball. 

 Fig. 216. The oenlroneUU'omi stage of tbo loop, x u. 



Fig. 217. A later stage; showing the resorption of the anterior portion of the loop. X 6. 

 Fig. 218. Early DiELASMA stage, produced by further resorption. X 6. 

 Fig. 219. Loop and hinge-plate of a mature specimen. X 6. 



Fio. 219. 



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

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

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

 and Centronella. 



DIELASMINA, Waagen. 1882. 



188'2. Dielastnina, Waauiui. Pi-oduutus-limestone Fossils ; Brachiopoda, p. 3ti9, 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. 



no. MO. 



Fio 221. 



SUlatmina pUctita, Waagen. 

 Dorsal and frontal views. 



(Waagen.) 



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

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



