ON DIPLOGRAPTID^, LAPWORTH. 273 



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 thecae 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 DiplograptidcB, 

 for so little of their internal structure is yet known, they may 

 have a collection of remotely related forms with thecae 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 geo- 

 logical section of the Student's Natural History Society, and 

 after I had nearly finished writing it, I received from S. L. Torn- 

 quist a copy of his work "Observations on the structure of some 

 Diprionidce y Sartryck af Kongl. Fysiografiska Sails Kapets 

 Handlingar. Ny foljd 1892-3, Bd. 4, Lund, 1893. Lund Univ. 

 Arsskrift, 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. internextis, Tqt., fig. 25, Diplograptus palmeus, Barr., 

 figs, 29, 33—35, and Ceplialograptus 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 



