66 Vie Ines (GOT ESE NG 
From all species of the genus except two or three, this species is distin 
guished by its small size. From the remainder by the undulating dorsal mar-- 
gin and the double series of “ pustules.” 
Didymograpsus perfiexus Gurley sp. nov. 
Branches diverging from a minute sicula at a variable angle, probably 
from 225° to 270°, variously directed subsequently from post mortem deflec- 
tion, gradually widening from their origin to a maximum width of 3™". Maxi- 
mum length observed (in a specimen whose width showed that it was situated 
far to the proximal side of other fragments, and that it could not have been 
near the sicula) 17. Coenosarcal canal narrow, occupying not more than 
one-quarter or one-fifth of the extreme width of the branch. Thece 20 to 25 
in 25™™, almost or quite straight, very wide in proportion to their length, 
little wider (one-quarter or thereabouts) at aperture than at base; inclined to 
axis of branch about 30°; apertural margin straight, destitute of spines, 
obliquely directed, 
Horizon and locality.—Upper Calciferous shales, Summit, Nev. 
This species presents itself under very many aspects, so many in fact that I 
shave several times suspected that two species were present. Subsequent study 
chas, however, led to the conclusion that probably all these formsare to be referred 
to differences in preservation conditions, that is that they are preservation 
facies. To start with the angle of divergence varies within very wide limits, 
being at one extreme about two, and at the other about three right angles. 
Several intermediate positions are present. The true angle was probably 
mearer the upper than the lower limit, the lowering resulting from subsequent 
(post mortem) bending of the slender polypary. This seems not unreasona- 
ble especially when the inclination of the theca in some specimens is less 
than the average, and these same thecz have every appearance of having 
been compressed backward against the virgula. Such pressure naturally 
tends to diminish the angle of divergence, measured as the latter is on the 
dorsal side. These two conditions (diminished angle and flattening of thecez) 
were not, however, observed on the same specimen. ‘The inclination of 
the thecz to the virgula (measured of course, on the distal side), seems to 
increase slowly, those on the distal portion being somewhat moreerect. They 
are also slightly more numerous ir a given space. Upon each theca at the 
distal corner remote from the virgula, is a circular pustule-like body which 
may have been an orifice in the lateral wall. 
This form probably approaches D. uzcholsont Lapw., and D. suecicus 
Tullb., more nearly than any others. The thece here are rather regularly 
22 to 24 in 25™™ as opposed to 25 to 30 (average 26) in the same space, in 
Lapworth’s species. Also D. xicholsonz differs in the somewhat rigid branch 
‘with a uniform width of about 1™™.25, and the concave thecal mouth usually 
prolonged into a denticle. With DY. swectcus its affinities would seem even 
