88 



NEW YORK STATE MUSEUM 



The first to observe a dilatation of the stem in a diplograptid was 



Barrande in Diplograptus pal me us [1850, p. 60]. He made the 



following observations (translated) : 



Most frequently the naked axis (nemacaulus) undergoes 

 a torsion which one recognizes by a pronounced strangula- 

 tion, beyond which one sees a large dilatation. In several 

 individuals we observe that this abnormal enlargement 

 manifests itself in the place of the last thecae of the adult 

 part, i. e. in the region where we have supposed the succes- 

 sive withering and shedding of the oldest zooids to have 

 taken place. Finally, various specimens show the naked 

 axis separating in two or four branches, which gradually 

 widen toward the extremity. 



In 1869 Nicholson described a Scottish form as I) . 



vesiculosus on account of "a long, fusiform, ovate or 



cylindrical vesicular dilatation " of the nemacaulus, "which 



is bordered by strong filiform margins." He states that 



this species always possesses the vesicle, while in others as 



tifs g ' ^efi'/ilus^s D- prist is and D. pal me us, it is but sometimes seen. 



Nicholson. Copy from p m • 1 i 



Lapwonh. Nat. size The " vesicles of D. vesiculosus seem indeed to be 



quite constant, for they have again been observed as a 



normal feature by Lapworth in West Scotland [1876, pi. 2, 



fig. 41] and in Ireland [1877, p. 133] and the same author 



has described in C. scalar is var. tubuliferus from 



West Scotland and Ireland, a form whose nemacaulus is 



stated to expand " into a long flattened plate or vesicle." 



In Nicholson's monograph of British Graptolites a like 



expansion is figured of Diplograptus folium [see 



text fig. 19]. 



Gurley has observed similar swellings of the nema- 

 caulus in Climacograptus parvus Hall, which was 

 described by him as C. phyllophorus in allusion to 

 these appendages ; and also in C. caelatus. In regard 

 to the former it is stated | [896, p.77]: 



The chief interest in the species lies in the "disk." This has the form 



Fig 1 Group of Dip- 

 lograptitlae with liila- 

 tations of nemacaulus. 



