HISTORY OF RESEARCH. Ixxvii 



presence of the initial cone-shaped body (the sicula) in all Graptolites, and he uses 

 the term " radicle" to "signify the basal median process," " whether this consists 

 of the solid axis alone, or of the solid axis along with the common body, or 

 simply of the investing envelope of the latter." 



(2) Funicle and (3) Central Disc. — Both these structures are described prac- 

 tically from Hall's point of view, and the former opinions held by Nicholson as to 

 the " float "-like character of the latter are adhered to. 



Chapter 0. — Reproduction and Development. — The various "ovarian vesicles" 

 previously described by himself are re-described, and he changes his previous title 

 of " G-rapto-gonophores" to the more precise hydroidal title of " gonothecse." 

 The peculiar sac-like bodies figured by Hall (18G5) and Hopkinson (1871) in 

 specimens of D. Whitfieldii and D. prvstis are considered by Nicholson to be also 

 reproductive in function. 



Chapter 7. — Zoological Position of 'the Graptolites. — (1) Mode of Existence. 

 The free-floating habit of the true Graptolite is strongly emphasised, and con- 

 sequently the systematic separation of the fixed Dendroidea from the true 

 Graptolites is considered inevitable. 



(2) Systematic Position and Affinities. — These questions are entered into very 

 fully, and the various points of resemblance and difference between the Graptolites 

 and (1) the Actinozoa, (2) the Polyzoa, and (3) the Hydrozoa are discussed in much 

 detail. The general conclusion reached is, that they " find their nearest living 

 allies in the Sertularians," and are "truly referable to the Hydrozoa," though they 

 " cannot be placed in any living group of the Hydrozoa." 



Chapter 8. — Geological Distribution. — -The author's general views of the range 

 and distribution of the Graptolites differ in no essential particulars from those 

 expressed in previous papers, and need not here be referred to. 



Chapter 9. — Genera. — The final chapter is devoted to a classification of 

 the Graptolites, and to a description of the various genera, which are thus 

 arranged : 



Class, Hydrozoa, Sub-class Graptolitida3. 



Section A. — Monoprionidge, Hopk. : (1) Graptolites or Gra ptolithus ; (2) Didymo- 

 gra psus (including Dicellograpsus) ; (3) Tetragrapsus ; (I) Dichograpsus ; (•'>) Logano- 

 grapsus ; (6) Pleurograpsus ; (7) Ccenograps us, Hall (= Helicograpsus, Nich.); (8) 

 Gyrtograpsus ; (9) Eastrites. 



Section B. — Diprionidae: (10) Diplograpsus ; (11) Glimacograpsus ; (12) Dicrano- 

 grapsus ; (13) Retiolites ; (14<) Trigonograpsus ; (15) Eetiograpsus. 



Section G. — Tetraprionidse : (10) Phyllograpsus. 



Section D. — Dendroidea: (17) Ptilograpsus j (18) Dendrograpsus ; (19) Callo- 

 grapsus ; (20) Dictijonema. 



Section E. — Incertas Sedis: (21) Thamnograpsus : (22) Buthograpsus ; (23) 

 Tnocaulis ; (24) Gorynoides. 



