610 



NEW YORK STATE MUSEUM 



Desmograptus cancellatus Hopk. (sp.) 



Plate3,flerure8 5-8 



D icty ograpt US (Desmograptus) cancellatus Hopkinson. Quar. Jour. 



Geol. Soc. 1875, 31:668, pl.36, lig.lla, lib 

 cf. Desmograptus macrodictyum Gurley. Jour. Geol. 1896. 4:83f 

 Dictyonema (Desmograptus) canceilatum Ruedemann. N. Y. State 



Paleontol. An. Rep't. 1902. p.570 



Description. Rhabdosome infundibuliform, beginning with a chitinous, 

 apparently nonsiculate basal expansion, and a short stem. Branches thick, 

 undulating, in the proximal part little flexuous and subparallel, distally 

 becoming gradually more undulating; foi-ming by coales- 

 cence and redivision in the proximal parts long narrow 

 meshes ; in the distal parts elongate to broadly oval meshes. 

 These are in the mature parts about twice as wide as the 

 branches and three to four times as long as wide. Branches 

 12 to 14 in 10 ram. Thecal apertures circular, not promi- 

 nent, appressed to branches, apparently closely arranged. 

 Dissepiments rarely observable. Bifurcation of branches 

 quite regular, leading to a regular gradual expansion of the 

 rhabdosome. 



Position and localities. Common in graptolite bed 7 

 of the Deep kill section (horizon with Diplograptus 

 dentatus and Climacograptus? antennarius) 

 D. cancellatus was described as coming from the Lower Arenig 

 of Whitesand bay of St David's, which is stated to be overlain by Middle 

 Arenig beds containing some of Hall's species of Tetragraptus, Callograptus 

 and Didymograptus, occurring here in the Tetragraptus beds. It would, 

 therefore, seem that the British species is considerably older than the Deep 

 kill form, referred to it. As, however, Trigonograptus ensiformis, 

 a typical species of the third Deep kill horizon, in which D . cancel- 

 latus occurs, is cited as having been found in the Lower Arenig of White- 

 sand bay, it is possible that at the latter locality the beds are inverted oi 



FiK. 81 Desmograp- 

 tus cancellatus 

 Hopkinson (sp.) Enlarge- 

 ment of part of specimen 

 reproduced on plate 3, 

 figure 7. Deep klU. x3.75 



