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4. situated theca of the opposite side, and not from a common canal.
5. The hydrozoma including the virgula has grown in two opposite directions.
6. The scicula is not imbedded between two branches grown together, but is free originally, and later is incorporated within the periderm.
7. The virgula is not double, and has two quite distinct phases of development.
8. To the virgula are occasionally attached the bases of the thecal partitions.
9. A common canal as progenitor of the thecæ does not exist.
10. A double longitudinal septum is not present.

It is not now my intention to assert that this organization is repeated in all the representatives of the family Diplograptidæ, for so little of their internal structure is yet known, they may have a collection of remotely related forms with thecæ arranged in two rows, but since this family is entirely or in the main a natural one, the deviation from the general plan of structure cannot be very great.

Eight days after I had announced the above before the geological section of the Student's Natural History Society, and after I had nearly finished writing it, I received from S. L. Tornquist a copy of his work "Observations on the structure of some Diprionidæ." Särtryck af Kongl. Fysiografiska Sälls Kapets Handlingar. Ny följd 1892-3, Bd. 4, Lund, 1893. Lund Univ. Årsskrift, tom XXIX.

The "connecting canal," which, according to Tornquist, unites the scicula with the "common cavity of the rhabdosoma," is that part of the first theca which grows downwards. The proximal end of Climacograptus scalaris, Lin., figs. 7-15, and 18-20, C. internexus, Tqt., fig. 25, Diplograptus palmeus, Barr., figs, 29, 33-35, and Cephalograptus cometa, Gein., figs. 39-41, show the identical structure which I have just described. The groove illustrated in figure 17 and mentioned on page 6 as "a narrow longitudinal groove as to the nature of which I am not