THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE IV. VOL. II. 



No. X.— OCTOBER, 1895. 



L — On Didymograptus, Tetragraptus, and Pstllograptus. 



By Dr. Gerhard Holm, 



Palaeontologist to the Geological Survey of Sweden, Stockholm. 



Translated from the original in Geol. Foren. i Stockholm Forhandl Bd XVII 

 Haft iii, No. 164, 1895, pp. 319-359. By G. L. Elles and E. M. R. "Wood', 

 Newnham College, Cambridge. 



(PLATES XIII AND XIV.)i 



THE knowledge of the internal structure and development of the 

 different forms of Graptolites is very incomplete, owing to 

 the unfavourable method of their preservation, Graptolites, in almost 

 all cases, being found embedded in shale. 



For more than ten years, however, I have been acquainted with 

 Graptolites which, exceptional though it may be, are embedded in 

 pure limestone, and are usually preserved in full relief; not un- 

 frequently also the chitinous substance is so well preserved, that the 

 polypary can be set free by dissolving the limestone with acid. 



The first Graptolites which, by this means, have been isolated 

 and studied by me, were Climacograptus KucTcersianus, nov. sp., 

 Holm, from a specimen collected by G. Linnarsson, near Kuckers, 

 in Estland, and now the property of the Geological Institution at 

 Upsala, and Betiolites Geinitzianus, Barr., in a limestone nodule 

 from Motala. I have since described the internal structure of the 

 latter, principally with the aid of the above-mentioned specimen.^ 

 In the same paper I have given an account of an improved method 

 of dissolving the matrix, b^^ means of which, for example, such 

 fragile objects as the connecting parts of the reticulate polypary of 

 Dictyonema cervicorne, Holm, and the fork-shaped, apertural spines 

 of the thecse, can be isolated. 



Since the above-mentioned time, I have constantly collected as 

 much material as I could obtain suitable for treatment by this 

 method, for the purpose of a closer study of the structure, develop- 

 ment, and affinities of Graptolites ; and I have now isolated many 

 thousands of specimens belonging to a great many forms of different 

 groups of Graptolites. 



1 The plates and page-illustration wUl appear with the second part of this paper 

 next month. 



2 Bihang K. Vet. Akad. Handl., Bd. 16, Afd. iv, No. 7, 1890. 



DECADE IV. VOL. II. — NO. X. 28 



