Speciks ok tiik Chemiino Group. 95 



Ohservatlonn. The teiuleiicy among Diutyosponges of prismatic founda- 

 tion to produce nodes upon the surface, manifests itself in two ways; these 

 nodes develop either along the prism-angles, as in Hydnocebas and Botbyo- 

 DicTYA, or on the prism-faces, as in Prisnwdlctya Conradi, Gonoylospongia 

 and Tylodictya. In the last named genus, however, the prismatic foundation 

 is almost completely suppressed, although the nodes show very much the same 

 irregular characters as in Gongyl. Marshi. 



The characters of Prismodictya Conradi have already been pointed out. 

 The single specimen known of the species shows, near the fractured upper 

 end, an obscure nodation on several of the sharp pi-ism faces. These are 

 gentle and regular convexities and concavities lying in alternating rows. 

 How irregular they may have become in later growth it is, of course, impos- 

 sible to say, but the most primitive form of the node in Gongyl. Marshi is 

 of more complicated shape than the nodes shown in Prism. Conradi, while in 

 the latter even these simple nodes appear at a distance from the basal point 

 which, in Gongyl. Marshi, covers nearly the entire growth of the sponge to 

 maturity. It seems quite clear that Prism. Conradi exemplifies a primitive 

 stadium of Gonoylospongia. 



HYDNOCERAS, Gonrad. 

 1842. Hydnoceras, Conrad. Journal Philadelphia Academy of Natural 



Sciences, vol. viii, p. 267. 

 1863. Dictyophyton, Hall. Sixteenth Ann. Rept. N. Y. State Cab. Nat. Hist., 



pp. 84, 87, 90, 91. 

 1874. Dictyophyton, Larkin. The Alfred Student (May), p. 53. 



1879. Dictyophyton, Schimper. Zittel's Handbuch der Palaeontologie ; 



Palaeophytologie, p. 69. 



1880. Dictyophyton, F. Roemer. Lethaea Palaeozoica, p. 128. 



1881. Dictyophyton, Whitfield. American Journal of Science, vol. xxii, 



pp. 53, 132. 



1882. Dictyophyton, Whitfield. Bull. No. 1, Amer. Mus. Nat. Hist., p. 10. 



1882. Dictyophytmi, Zittel. Neues Jahrb. fiir Mineral., etc., vol. ii, p. 203. 



1883. Dictyophyton, Barrois. Ann. de la Soc. Geol. du Nord, vol. xi, 



pp. 80-86. 



1883. Dictyophytmi, Hinde. Cat. Fossil Sponges British Museum, p. 130. 



1884. Dictyophyton., Hall. Thirty-fifth Ann. Rept. N. Y. State Mus. Nat. 



Hist., pp. 466, 472, 473. 



