IV 



MISCELLANEOUS STUDIES IN DEVELOPMENT 



1. DEVELOPMENT OF A PALEOZOIC 

 PORIFEROUS CORAL* 



(PLATES XXVII-XXXI) 



THE origin and affinities of many groups of Paleozoic 

 corals are still obscure. The main elements of the recog- 

 nized system of classification seem to be stable, yet so little 

 is known of the growth and structure of a number of impor- 

 tant groups that they occupy a different place in almost every 

 arrangement of the genera. Each fact of development affords 

 data which eliminate, to a degree, the want of knowledge 

 concerning their origin and relations. Unless the growth 

 of the organism is obscured by pronounced accelerated or 

 degradational features, its interpretation is simple and 

 throws much light on its ancestral history. Paleozoic types 

 in general are least modified in their development by accel- 

 eration. They usually show some marked expression of their 

 prototype, and also the succession of changes through which 

 they have passed during their evolution. 



The species here discussed was originally described as 

 Michelinia lenticularis Hall,f from the Lower Helderberg 

 Group of New York. If Michelinia is entitled to recognition, 

 it will exclude this form, as it is without tabulae. Pleuro- 

 dictyum, as now defined, is more in harmony with these 



* Trans. Conn. Acad. Sci., VIII, 207-214, pis. ix-xiii, 1891. 

 t Twenty-sixth Rept. N. Y. State Mus. Nat. Hist., 113, 1874. 



