Any observations which can throw light on the systematic position of the Graptolitidœ are of great importance. That these anomalous fossils are Zoophytes, in the wide sense of the term, is almost universally conceded; the diffculty is in determining whether they are cœlenterate or molluscoid. Those who have described the members of the family have almost invariably considered them to be hydrozoa, and it must be allowed that in general aspect they very much resemble Plumularia and Sertularia. But when their structure is examined it will be found that they widely differ from any known hydrozoon, and especially in that the entire polypidom is composed of the different polype-cells, without any distinct common canal. Sometimes the polypes rise from a common substance which extends along the whole of the celluliferous portion of the organism, but there is no constriction or septum at the base of the cells, cutting off this common substance from the individual polypes. This is the structure of Graptolitus priodon, Bronn. In other species the walls of each cell seem to be continued to the solid axis, as is the case most probably in Graptolitus sagittarius, L. and certainly in some the species with a double series of cells, as Diplograpsus folium, His. D. pristis, His. and D. cometa, Gein. The mouths of the cells are frequently furnished with one or more long spines, as in some species of Bastrites, and in Diplograpsus pristis, His. In these characters the graptolites show a greater affinity with the polyzoa. Compare the genera Scruparia and Bicellaria. But there are some peculiarities which do not well agree with the living forms of either section zoophytes. Among these may be mentioned first the prolongation of the solid axis in both the unilateral and bilateral forms beyond the celluliferous portion in the newer part of the polypidom, and then their free polypidoms, for neither the spines which terminate the older portion of some species of Diplograpsus nor the slender base of Dendrograptus linearis, Car., could be radicles, and the species of the genus Graptolitus have no indications of a hydrorhiza from the older extremity.