158 J. HOPKINSON ON BRITISH GRAPTOLITES. 



Sub-Kingdom, C^lenterata. Class, Hydrozoa. 

 Order, Graptolitid^. 



Family I. Monoprionid^. Polypary with a single series of 

 liydrotlieca3. 



Genus 1. Rastrites, Barrande (Grapt. de Boheme, p. 64). 



Polypary simple (unbranched), consisting of a slender tubular 

 periderm supporting linear hydrothecje, free througbout their whole 

 length. E. peregrmus Barr. (PL viii., /. 1) is the typical species. 



Genus 2. Graptolithus, Linnjeus (Systema Natura3, Ed. 1). 



Polypary simple, consisting of a tubular periderm supporting 

 hydrothecae in contact for more or less of their length. G. prtodon, 

 Bronn (PL viii., /. 2), and G. Hisingeri, Carr [PL viii., /. 3), are 

 widely distributed species. I also figure one of the many varieties 

 of G. Sedgwickii, Portl. (PL viii., f. 4). It bears some resem- 

 blance to G. Salteri, Gein., to which I at first referred it. 



Genus 3. Cyrtograpsus, Carruthers (Murch. Sil, Ed. iv., p. 540). 



Polypary compound, growing in one direction from the proximal 

 end, and consisting of a periderm giving off branches from the 

 side on which the hydrothecje are developed. The branches re-branch- 

 ing in a similar manner. C. Murchisoni, Carr., is the only species 

 of this genus (PL viii.,/. 5). 



Genus 4. Didymograpsus, McCoy (Brit. Pal, Fossils, p. 9). 



Polypary consisting of two simple branches, growing bilaterally 

 from the radicle, and bearing hydrothec£e on the margin opposite 

 the radicle. " The branches of the polypary sometimes extend at 

 right angles to the initial process, sometimes they are bent back- 

 wards upon it, and less frequently they are turned- inwards from it." 

 (Carruthers.) D. Murchisoni, McCoy, is a characteristic species 

 (PL viii., /. 6). 



Genus 5. Tetragrapsus, Salter(Journ.Geol. Soc.,vol.xix.,p.l35). 



Polypary consisting of four simple branches, growing bilaterally 

 from a short hydrocaulus which is sometimes invested with a 

 corneous disc. T. hryonoides, Hall (PL viii.,/. 7). 



Genus 6. Dichograpsus, Salter (Geologist, vol. iv., p. 74). 



Polypary growing bilaterally and branching regularly, the 

 hydrocaulus or non-polypiferous base of the branches invested with 

 a corneous disc. D. octohachiatus, Hall (PL viii.,/. 8). 



Genus 7. Cladograpsus, Carruthers (Trans. R. Phys. Soc, 

 Edin., 1858, p. 467). 



