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BISCAYAN PLANKTON. 



Part IV.— THE THALIACEA. 



By G. Herbert Powler, B.A., Ph.D., F.L.S., F.Z.S. 



(Plates 8 & 9.) 



Bead 2nd March, 1905. 



Contents. 



i. CrcLOMVAEiA. Tago 



a. Gonozooids. Doliolum Tntonis, Herdman 89 



Doliolum Kroliiii, Herdman 90 



Doliolum Nationalis, Borgert 90 



Doliolum sp., Borgert 90 



h. Phorozooids. Doliolum Tritonis, Herdman 91 



Doliolum sp., Borgert 91 



c. Blastozooids. A (? = Z). Tritonis, Herdman) 93 



B 97 



Doliolum Krohni, Herdman 97 



d. Trophozooids. A (? = Z). Tritonis, Herdman) 97 



B 9S 



ii. Hkiiimtakia. 



Sulpa rxmcinata-fusiformis, Cham. Cut 99 



Salpa echinata, Herdman 99 



Salpa democratica-mucronata ?, ForskPil 99 



i. THE CYCLOMYARIA. 



This suborder was represented only by known species of Doliolum, but the collection 

 contained four apparently undescribcd phases, two of which I believe to be the blasto- 

 zooid and trophozooid * of Doliolum Tritonis. Of the four polymorphic life-phases of 

 Doliolum, the gonozooids alone have been adequately described for most species ; in a 

 recent account of the genus, Dr. Borgert t gave a synoptic table which covered the 

 gonozooids of all admitted species, but he did not attempt it for any other of the three 

 forms presented by this remarkable organism. It will be most reasonal)le, therefore, to 

 begin with the gonozooids ; to pass to the phorozooids (since they are stated to be 

 structurally identical with the former, except internally for the absence of the generiitivc 

 organs, and externally for the presence of the ventral outgrowth on which the gonozooid- 

 buds are borne and for the absence of the dorsal outgrowth) ; and to conclude with the 

 blastozooids and trophozooids. 



a. Gonozooids. 

 Doliolum Tritonis, Herdman. 



This occurred at all depths down to 100 fathoms, but never below that horizon ; it is, 

 therefore, epiplanktonic. But it did not occur in sufficient numbers (111), nor on 



* Blastozouid = Amme. rhorozooid = rtlrgcthicr. Trophozooid = Niihrthicr. Gonozooid = Geschlechtsthicr. 

 t A. Borgert : ' riankton-Expcditiou. Thaliacca.— C. Vcrtheilung der Doliokn.' 1 lollow his synonymj-. 

 SECOND SERIES. — ZOOLOGY, VOL. X. 15 



