cviii BRITISH GRAPTOLITES. 



In Pomatograptus the polypary is straight or concavely curved, the cells free 

 at their outer end, while the aperture is small and protected by a roof-like 

 process arising from the upper part of the cell. 



Under the name Pristiograptus the author describes P. bohemicus, P. Boemeri'?, 

 /'. Nilssoni, P. colonus, P. testis, and a new species P. frequens. Under the name 

 Pomatograptus, he describes P. priodon, V. Becki, P. Barrandei, and a new form, 

 P. micropoma. 



The structure of Betiolites is also described. 



Mode of Life. — In discussing the mode of life of the Graptolites, Jaekel 

 returns to the idea of their rooted attachment to the floor of the sea, and also 

 revives the opinion of Hall that all single Graptolites " usually described under 

 the name Monograptus" are torn-off pieces of larger colonies. He maintains that 

 the narrow end is never complete, and never shows well-developed cells. 



Affinities. — Jaekel agrees with Neumayr that the Graptolites should be placed 



in a special class, which might be compared with the Corals. 



1890. During this year, a brilliant paper on the minute struc- 



Holm ' ture of the Graptolites was published by the Swedish palaeon- 



"GrotlnudsGraptoliter,'' . n 



. T.-i t^ c, i tologist, Holm. 

 ' Biliaug K. Sveuska 6 ' 



Vet-Akad Handl ' bd Previous researchers had attempted to isolate the Grapto- 



xvi, af. 4, no. 7. lite from the rock in which it was imbedded, but the process 



was brought to great perfection by Holm, and the value 

 of the results thus obtained can hardly be over-estimated. In this paper 

 (" Gotlands Graptoliter ") Holm gives the results of his investigations of the 

 structure of Dictyonema, Monograptus dubius, Betiolites, and Stomatograptus. 



Dictyonema cervicorne. The structure of a branch of Dictyonema is worked 

 out in this new species. The thecas are turned inwards. From one side of the 

 thecas, alternately on the left- and right-hand side, there grows out a " bird-nest "- 

 like theca, which Holm terms a " bitheca " (? gonangium). Between each pair of 

 thecas there is one dissepiment. Holm points out that the forms referred to the 

 genus Dictyonema are both siculate and non-siculate, and holds that it may be 

 found necessary in the future to sub-divide this genus. 



M. priodon and 71/. sub-conicus are recorded from Gothland, and M. Flemingii 

 (which he regards as only a mutation of M. priodon) and M. dubius are figured. 

 The structure of the latter species is very accurately represented. 



Betiolites Geinitziauus . The isolation methods adopted by Holm also enabled 

 him to give a far more complete description, and a more detailed and perfect 

 figure of the structure of Betiolites than had hitherto been possible. The nature 

 of the outer net-like periderm is more particularly elucidated, as well as the 

 relations between the straight and zigzag " virgulas," and " threads " of the 

 skeleton generally. 



Stomatograptus Tornquisti. Many further points of structure, obscure in 



