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THE JOURNAL OF GEOLOGY.

scicula has been already described. This part like the scicula grows towards the proximal end. The distal portion of the virgula does not begin to develop until the scicula has been taken into the hydrosoma. It is likewise stouter the further it is removed from the point of the scicula. As it has its origin in the union of the longitudinal lines of the distal portion of the scicula, it appears very probable that the entire distal part of the scicula, also, first had its inception when the scicula is taken into the hydrosoma. Accordingly, the scicula, when it was yet free, would have been either open on the distal end or it had a very thin wall which disappeared later. The first shell-layer, therefore, was a small simple ring.

Here and there, quite irregularly, the virgula fastens itself to the above-mentioned swellings on the proximal ends of the thecal partitions (Pl. II., figs. 11-12). In figure 10, it is entirely free. In diagnoses of diplograptids, it is often mentioned that the virgula extends beyond the distal end. This need not be accidental in a species of this nature, since in forms where the virgula is not fastened to the diagonal swellings, it has a greater chance of being preserved, even if the periderm is broken away. If the virgula is regularly attached to every partition, it can only become protruding under very favorable circumstances. In this species, I did not see the virgula protruding.

A common canal as progenitor for all thecæ does not exist. The partition walls between the thecæ, moreover, join so closely on the center of the hydrosoma that the virgula hardly has sufficient space to straighten itself.

A longitudinal septum is not present.

In summing up the results of my investigations, the following points are shown:

  1. The scicula consists of two parts, is basally open, and bilaterally symmetrical.
  2. From the scicula there sprouts but one bud. This Diplograptus is therefore monoprionidian.
  3. This bud does not develop into a canal, but into a theca.
  4. Each theca comes forth from the next more proximally
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