NORTH AMERICAN GRAPTOLITES 7% 
introverted, opening well within ventral margin of the polypary, the free 
portions occupying about one-fifth of entire length of theca. Excavation dis- 
tinct, deeply curved, occupying about one-third of transverse diameter of 
polypary, the interspaces taking up less than one-fifth of the ventral margin. 
This form certainly belongs to a group of Dicellograpsi comprising besides it 
three species as yet undescribed. All these forms agree in having thece of the 
same general type, with very short, isolated distal portion and small introver- 
sion; but they differ in size, length, and angle of divergence of the branches, 
and in the proportion of their thecee. They are, however, all of the same 
geological age, and it is not outside the limits of possibility that they may be: 
local representative forms of one and the same species. 
The whole group is intimately related to the group typified by D. forch- 
hammer? (Geinitz), into which it passes by almost insensible gradations. 
Horizon and locality.—Lower Dzcellograpsus zone, Stockport, N. Y. 
Dicellograpsus elegans (Carr). 
Specimens occur in our Lower Dicellograpsus zone which agree in every 
respect with Carruther’s species except that they show 24 to 28 thece in 25™™,. 
while Carruther’s and also Lapworth’s figures show but 20 to 22. 
Horizon and locality.—Lower Dzcellograpsus zone, Stockport, N. Y. 
DICRANOGRAPTUS HALi, 1865. 
Can. Org. Rem., Dec. II., p. 112. Type, D. vamosus (Hall). 
Besides D. furcatus two types of this genus occur in American strata, viz., 
D. nicholsont ,Hopk., with a very short proximal portion bearing very few 
thecee (ad plurimum 8 or g) and LD. ramosus (Hall), with a much larger proxi- 
mal portion bearing nearly twice as many thecz (usually 15 or thereabouts). 
Of VD. nicholsonz 5 (perhaps ultimately reducible to 4) fairly well marked 
varieties occur which present a gradation from the non-spinose var. arkansas- 
enszs with an angle of 135° to go° through D. nzcholsonz (angle 80° to 70°) to 
the smaller angled spinose forms w/ztianus and parvangulus and finally to 
var. diafason with converging branches. 
D. vramosus presents 2 varieties, the typical form with a stout polypary, 
occurring in the Lower Dicellograpsus zone and a much more slender variety 
occurring in the Upper Dicellograpsus zone at Magog. 
Dicranograptus furcatus (Hall). 
This species presents a very peculiar structure. In the compressed state 
it consists of several elliptic loops. The thecz begin on the proximal, diprion- 
idian portion, and are continued on the ow¢er side of the Zower half of the first 
loop. At the middle of the loop they become scalariform and on its “per half 
occupy the zzzer margin of the branch. Traced upward, on to the next loop, 
they are seen to be (owing to the recurving of the branch toward the median 
