42 The American Geologist. Juiy.isoi 
Dictyonema cervlcorne (sp. n.) Monograptus subconicus, Tornq, 
Dictyonema abnorrae (sp. n.) Monograptus dubius, Siiss. 
Monograptus priodon Bronn. Monograptus sp. 
Monograptus priodon var. llciningii, Retiolites gt^initzianus, Barr. 
Salter. Retiolitcs nassa(sp. n.) 
Following in the track of Dames' and Broggor's researches the author 
discusses the structure of the genus Dictyoneiivi. Particularly apt 
seems to us his views regarding the heterogeneous nature of the species 
usually referred here. For e.xample we find in this genus a species 
(D. jtahelllfoi-rne) which is undoubtedly siculate, associated with species 
most of which are probably, and some of which are certainly not so. 
As he remarks the ( for graptolites) unprecedented vertical range of the 
genus furnishes additional reasons for suspecting some of the generic 
references. We may, however, note that the siculate and non-siculate 
types occur at one and the same horizon. But a generic division cannot, 
as Mr. Holm says, be satisfactorily establislied until the species are 
more thoroughly known especially in the proximal portion. 
Under the description of D. cervicorne we are introduced to one 
of the most beautiful elucidations of graptolite structure that we 
have ever seen. The author imbedded a specimen in Canada balsam 
fac&down upon a slide, and then removed the limestone matrix by solu- 
tion with acid. Part of the wall of the funnel-shaped polypary was 
thus obtained in full relief with the parts in their normal relations. 
The thecffi are seen to form one vertical row and to terminate in a 
long hay-fork like spine. Situated alternately on the two sides of 
these spines ( and thus forming two vertical rows) are peculiar cup- 
shaped bodies, ( " by-thecae " ) which are compared by the author to 
bird's-nests. They are divided from the thecte by a wall. It could not 
be ascertained whether any connection existed between these by-thecte 
and the adjacent theca?, or whether the former communicated with tlio 
common canal. He suggests that they may be fjoiuimjia. It is owing 
to this arrangement of the thecie in one vertical row along the inner 
face, and of the by-thec;ie in two vertical rows along the lateral faces of 
the branch that when looked at from the side the branches appear 
serrate on account of the thecae and when looked at from without the 
theca; are invisible being hidden by the branch, which latter presents a 
zig-zagged appearance owing to the alternately projecting by-thecte on 
either side. The connecting cross-filaments are shown to be flattened 
from above downward. They are bow-shaped with the convexity out- 
ward andpossess a pitted surface and outwardly projecting branches. 
They correspond in number to the thecie beween each pair of which 
they project. 
Not less beautiful than the foregoing demonstration is that of the 
structure of the polypary in RetloUtes geinitzianus and Stomatograptus 
tornquistl.* 
In the former species we see two virguhe (the one straight and the 
other zig-zag) occupying the central line of opposite faces of the 
'Altiiougli many of these points liave been previously noted, this ilescription is 
wortlijr of mention as it is almost the first hased upon tlioronglily satisfactory 
material. 
