592 NEW YORK STATE MUSEUM 



recognized the graptolite nature of Dictyonema in spite of its diiferent habit 

 [1865, p.l36]. 



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

 repeatedly 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 e 1 1 i f o r m e , at the 

 initial part of the rhabdosome, and the basketlike or conical 

 shape of the latter, as well as the position of the thecae on 

 the inside of the basket. 



But tlie complicated structure of the branches was 

 Fi8.3i mctyone- j^ot suspectcd till Holui in 1890 described in D. cervi- 



macervjcorne i 



Holm. Shows the n ,i tt cim • • /^ j_i i i 



uppermost thecae come, trom the Upper feiJuric m (xotland, appendages 



of two adjoining- x j. o 



ISiikf- ""pL^m to the thecae, shaped like birds nests [text flg.21] 



and nestlike by- i • i i i i • i , •^ ^ ^ ■ ttt- 



uiecae or^^gonangra. ^yhich hc thought might possibly be gonaugia. Wiman 

 ^"^ succeeded in isolating the rhabdosome and obtain- 



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

 strated that the branch consists of three different kinds of individuals 

 [.§<?(? sections, text figure 23 copied from Wiman]. These he denotes as 

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

 correspond to the thecae in the Graptoloidea, Imdding individuals (k, k^, 

 kg etc.) and sexual individuals or gonangia (g, g^, gg etc.). The budding 

 individuals [see section 6], Avhich 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 (o'ectius Nematophoreii)} 



^ Wiman 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. 



