1^8 NEW YORK STATE MUSEUM 



glass Sponges in the Chemung fauna, and the genus Dictyospongia, 

 which expresses it, is not only freely developed in species but its 

 individuals are often of commanding size and graceful form. 



It was also indicated in the study of these fossils that the 

 smooth, obconical shape being primitive, the nodose structures of 

 the surface appeared as a secondary character. Such evidence, how- 

 ever, was not, at the time of the preparation of the work cited, 

 regarded as altogether conclusive. 



It was further observed in connection with the study of the 

 interrelations of these sponges, that the large series of annulated 

 forms known as Ceratodictya stood in somewhat similar relation- 

 ships ontogenetically to the smooth cones, as did the nodose species ; 

 that is to say, the secondary conformation of the surface begins to 

 express itself either as nodes, or as rings, or as a combination of 

 both together. We must here note a third consideration, and that 

 is the series of prismatic or banana-shaped sponges, Prismodictya ; 

 a large tribe of very effective, compact and graceful appearance, 

 in which the prismatic sides are developed with rarely any indica- 

 tion of nodosity or annulation. These prismatic sponges also, are 

 found to develop their prismatic faces as a secondary feature, the 

 incipient part of the sponge or its infantile condition being still of 

 the smooth, obconical pattern. 



We have then three different secondary modifications superim- 

 posed upon the primary expression of these sponges, all of which, 

 in combination or independently, are competent to produce and 

 have produced a very extraordinary variety of generic and specific 

 expressions. The exact order of succession in these features 

 should be established, if this is possible. Inspection of a very 

 large amount of material does positively indicate the development 

 of the prismatic form of the skeleton before the appearance of 

 either rings or nodes, and of the other two it is reasonably safe 

 to say in a general way, that the tendency to nodes manifests itself 

 earlier than the transverse constrictions which produce the annula- 

 tions. The normal order of time and succession therefore, in the 

 development of these three characteristics from the simple, smooth 

 obcone, is first the prisms, second the nodes, third the rings. In 

 terms of this ontogenetic succession it is therefore possible to esti- 

 mate any species of these various types of the prismatic, nodose 

 and ringed Dictyosponges and their combinations, in terms of 

 stationary, arrested, or accelerated development referable to the 

 standard type of the simple, smooth skeleton. 



