'><!)2 NEW YORK STATE MUSEUM 



recoguized the graptolite nature of Dictyonema in spite of its different habit 

 [1865, p.l36j. 



Since Hall's brief description of the genns, its characters have been 



i-epeatedly discussed, specially by Nicholson, Dames, Brogger, Tullberg and 



Mattliew. These observers have established the fact of the presence of a 



sicula in several forms, as in D . f 1 a b el 1 i f o r m e , at the 



W yU initial part of the rhabdosome, and the basketlike or conical 



M A shape of the latter, as Avell as the position of the thecae on 



7yi#^ the inside of the basket. 



w r But the complicated structure of the branches was 



Fig.2i Dictyone- rot suspccted till Holm in 1890 described in D. cervi- 



macervicorne r 



Holm. Shows the j. .1 -r-r o'l • • /~i xi j j 



uppermost thecae corue, irom the Upper feilunc in (Gotland, appendasres 



of two adjoinini? ' ^ ' j. x o 



I'Skf- "pr'ic^' to the thecae, .shaped like birds nests [text fig.21] 



and nestlike by- i-iii 1 -i -iii • -itt- 



niecae cg^^gonangm. which he thought might possibly be gonangia. Wiman 

 *"" succeeded in isolating the rhabdosome and obtain- 



ing thin sections, by means of which [1895 and 1896J he has demon- 

 strated that the branch consists of three different kinds of individuals 

 [see sections, text figure 23 copied from Wiman]. These he denotes as 

 nourishing individuals (his thecae, t, ti, t^ in sections), since they doubtless 

 correspond to the thecae in the Graptoloidea, budding individuals (k, kj, 

 kg etc.) and nexual individuals or gonangia (g, gi, g^ etc.). The budding 

 individuals \_see section 6j, which do not open outward, produce three 

 individuals by gemmation, one of which is again a budding individual, 

 while the second is a theca and the third a gonangium. All the indi- 

 viduals are, according to Wiman, formed in this way. Freeh [1897, p.571] 

 expresses the view that the so called gonangia of Holm and Wiman are 

 comparable to the nematocalyces of the Hydrozoa, by adding behind 

 gonangia (rectius Nematoplioreii)} 



^Wiraan has in a later paper [1900, p.l88] pointed out in defense of his view that 

 the nematocalyces occur in pairs, while but one gonangium is found associated with a 

 theca, and further, that the nematophores, as defensive polyps, have as a rule an exposed 

 position while the organs considered by him as gonangia are found in protected positions. 



