3<D2 NEW YORK STATE MUSEUM 



Dicellograptus intortus Lapworth 



Plate 18, figures 9, 10 



Dicellograptus intortus Lapworth. Ann. & Mag. Nat. Hist. Ser. 5. 1880. 



5: 161; pi. 5, fig. 19a 

 1 ) i c e 1 1 o g r a p s u s intortus polythecatus Gurley. Jour. Geol. 1896. 4: 70 

 Dicellograptus intortus Fearnsides. Section C. Belfast 1902. separate, p. 1 

 Dicellograptus intortus Clark. Geol. Mag. Ser. 4. 1902. 9:498 

 Dicellograptus intortus Elles & Wood. Monogr. Brit. Grapt. pt 4. (Pal. Soc. 



1904.) p. 146, fig. 90a, b; pi. 20, fig. a-f 



Dr Gurley has in 1896 listed a form from Stockport as D. intortus 

 polythecatus var. nov., stating that it resembles Lapworth's species in 

 the mode of growth, character of thecae and dimensions of branches, but 

 differs in having more thecae in a certain space (32 in 25 mm), the first six 

 or eight of which bear spines almost as long as the thecae, and the mode of 

 growth of Dicranograptus furcatus. The latter form it is said to 

 resemble somewhat when the proximal portion of the rhabdosome is absent, 

 but D. furcatus has "thicker branches (1 mm as against .6 for the 

 present form), the thecae are much coarser and are all provided with strong 

 spines. The loops are also more elongate and narrow." 



We have not been able to find either Gurley's types of this variety in 



the Stockport collection, nor any drawings of the same in his manuscript. 



Several specimens from Stockport (here reproduced in 



plate 18, figures 9, 10) agree with the description of D. 



intortus Lapw., given in the Monograph of British 



222 ^f~ Graptolitcs. From this latter description and the 



Fig. Li, 222 Dice'io- excellent figures accompanying it, it appears that the 



grapt us intortus Lap- 



Sdosomes! la euiarged' ,S x t thecae in the British form number from 11 to 14 in 10 



Figuve 22i. that of original of , 



pi.uc- is, figure 9 mm ( 28-35 in one inch) and that they also possess spines 



at the proximal end. This would leave as the only difference the mode 

 of growth, whose validity has been rightly doubted by Gurley himself 

 in his description. It is therefore probable that there cannot be found 

 sufficient differential characters for varietal distinction in the American 

 form. 



