NORTH AMERICAN GRAPTOLITES 67 
closer, but in that species we have somewhat crooked theca, twice or one 
and one-half times as wide at mouth as at base, with the somewhat concave 
mouth often bearing a denticle. 
Didymograpsus geminus (Hisinger). 
(Miller’s North American Geology and Paleontology, 1889, p. 186, Fig. 
169.) 
Concerning this form, it may be remarked (1) that Hisinger’s gemznus 
(Lethaea Suecica, Suppl. 2, 1840, p. 5, Part XXXVIII., Fig. 3) is a syno- 
nym for D. murchisont Beck (Murchison’s Sz/urzan System, Part I1., 1839, p. 
694, Plate XXVI. Fig. 4); (2) that D. murchisoni is not known to be Ameri- 
can (except as var. furcillatus Lapw.; see p. 4); and (3) that the original of 
Miller’s figure is Carruther’s mal-identification (in Murchison’s Sz/urza, 4 
ed., 1867, Plate IV., Fig. 8)as D. geminus His., of D. fatulus Hall. 
Didymograpsus hirundo Salter, 1863. 
Quar. Jour. Geol. Soc. London, XIX., p. 137, Fig. 13. 
Graptolithus constrictus Hall, 1865, Can. Org. Rem., Dec. II., p. 76, 
Pilate). ies. 23-277. 
This species is very largely represented in collections from the main Point. 
Leviszone. The supposed constriction of the theca mentioned by Hallis clearly 
an illusion, due to the intervention of a thin film of shale which covers one 
theca along the furrow produced by the overlapping apertural margin of the 
next proximal theca. This produces an appearance as though the distal 
theca were interrupted and contracted to receive the next proximal one. 
Specimens in relief show the thecze uncontracted. 
Didymograpsus convexus Gurley, sp. nov. Plate V., Fig. 8. 
Branches slender, in distal portion 1™™ wide, diverging from a small sicula 
with an upwardly concave-rounded curve, including between them (on the 
dorsal side, of course) an angle of about 265°. Thece 20 to 22 in 25™™, 
inclined to axis of branch 25° to 30°, widest at mouth, with a straight, aper- 
tural margin; the last making (on the distal side) an angle with the virgula 
of 105° to 110°; thecze free for one-half their length. 
Only two specimens were seen, but the aspect is such that they cannot be 
referred to D. serratulus or any other described species. Possibly it may be 
the proximal portion of D. sagztticau/is, but nearly fifty years have passed 
since the discovery of that species without the finding of any specimens long 
enough to connect the distal and proximal parts; hence the necessity for two 
names, at least pending the proof of such a connection which may be long 
delayed. 
This species may be recognized by the broadly rounded curve at the base. 
Horizon and locality—Lower Dicellograpsus zone, Stockport, N. Y. 
