272 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, there- 

 fore, 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 (PI. II., figs. 11-12). In figure 10, it is entirely free. 

 In diagnoses of diplograptids, it is often mentioned that the vir- 

 gula 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 thecae does not exist. 

 The partition walls between the thecae, moreover, join so closely 

 on the center of the hydrosoma that the virgula hardly has suf- 

 ficient space to straighten itself. 



A longitudinal septum is not present. 



In summing up the results of my investigations, the follow- 

 ing 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 Diplo- 

 graptus 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 



