NORTH AMERICAN GRAPTOLITES 73 
angle (35° or 40° against 70° to 80° in the Utica specimens) and in the pres- 
ence of short, rigid spines on the thecze of the stem and on practically all 
those of the branches. In the latter features lies its chief difference from var. 
parvangulus Gurley. I should add that a careful examination of the type 
specimen shows the proximal portion to be longer than shown in White’s fig- 
ure, at least six thecee being visible. 
Dicranograptus nicholsoni parvangulus Gurley. 
(D. nicholsoni Lapw., 1876, Armstrong, Young & Robertson’s Cat. West. 
Scot. Foss., pp. 6-9, Plate III., Fig. 79; 20., Lapw., 1877, Ann. Rep. 
and Proc. Belfast Nat. Field Club, I., p. 141, Plate VII., Fig. 2.) 
Dicranograptus nicholsont parvangulus Gurley, 1892. 
Ann. Rep. Geol. Surv. Ark. for 1890, III., p. 417. 
In the Stockport collection several examples of this variety occur which 
permit of the following description: Proximal portion about 6™™ long; at 
base 1™", and immediately below bifurcation 1.5" wide ; with eight or nine 
thece, each with a short, sharp horizontal spine ; branches 1™™ wide, diverg- 
ing at an angle of 35° or 40° (or thereabouts), often bending very slightly 
towards one another immediately after the division, thus producing a slightly 
rounded, bulging appearance. Thecze forming bent tubes, as in D. 22cholsont 
proper; as nearly as possible 24 in 25™"; those on the proximal portion and 
the first few on the branches above the bifurcation spiniferous. On the 
branches not more than three spiniferous thecz were seen. 
Horizon and locality.—Lower D¢cellograpsus zone, Stockport, N. Y., and 
in Arkansas ; Upper Dicellograpsus zone, Magog, Canada. 
Professor Lapworth (letter, 1890) remarks the difference between this 
form and D. nicholsonz, saying that this, the Glenkiln (= Lower Dicellograpsus 
zone) form, has a smaller angle and spinose proximal thece. D. mchclsonz 
proper is not found below the Utica. This variety, on the contrary, ranges 
through both the Lower and the Upper Déce/lograpsus zones but apparently 
not into the Utica. 
Since publishing this variety, I have noticed its extremely close resem- 
blance to D. whitéanus Miller. Indeed the latter form appears to differ from 
the present one only in having all of the thecze on the branches spinose. I 
might at this time unite the two forms were it not that var. w/z¢zanws rests upon 
a single specimen from a very far distant locality, and it is possible that fur- 
ther collections in Nevada may show the distinctive characters of w/z¢zanus 
to be sub-constant. Finally it may be noted that none of the eastern, or of 
the Arkansas specimens show any decided approximation to the condition 
found in whztianus. 
Dicranograptus nicholsont diapason Gurley, var. nov. 
Proximal portion with three minute spines at base; measuring from base 
