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BISCAYAN PLANKTON. 



Part III.— THE CH.ETOGNATHA. 



Bti G. Herbert Fowler, B.A., Ph.D., F.L.S., F.Z.S. 



(Plates 4-7.) 



Read 2nd June, 1904. 



^^'CTTn. 



Contents. 

 Pase 



The Systematic Determinatioa of Chsctognatha .... 55 



Examinatiou of the ' Research ' Specimens 58 



Sac/itta serratodcntata, Krohii 58 



Sm/ittafurcata, Steinhaus , 03 



Sac/itta macrocephala, sp. n 65 



Sayitia zetesios, sp. n 67 



Sagitta hipiinctata-, Quoy et Gaimard 69 



Sar/iita decijuens, sp. n 70 



Sa<j>tta sp. indet. ? juv 71 



Sagitta 1 planctonis, Steinhaus 71 



Page 



Sagittce spp. indet. of hexapterine type 73 



Krohnia hamata, Moebius 7-4 



Krohnia hamata, Moebius, var 77 



KroJmia subiiUs, Grassi 78 



General Remark.s on the Vertical Distribution .... 79 



Summary of the Observed Distribution 82 



Table of the Occurrence of the commouer Forms .... 84 

 Appendix : Chaetognatha from the Falkland Islands . 85 



Literature 85 



Explanation of the Plates 86 



On the Systematic Determination of Ch.etognatha. 



BISCAYAN PLANKTON : Part III. CHiETOGNATHA. 

 (Trans. Linn. Soc, Ser. 2, Zool. x. 55-87.) 



Temporary correction-slip. 



Add : " III the measurements of ' total length' and of ' tail-segment/ 

 the tail-fin has been included, greater accuracy with less damage 

 to the specimen being attained thereby." 



Fo7- " body " read " trunk." 



Add: "A slight short thickening of epidermis beiiind the head, 



scarcely enough developed to be termed a collarette." 

 For " body " read " trunk." 



For " usually " read " unusually.' 



'^ I'ernapS tniS sweeping ^tUlt;lUCllL may w? nvau i/w A\/xjM.«w jw^v...»w»...... p ^.-j. , . , ^ 



measurements showing the tail-segment of a species to be 24 per cent., or nearly a quarter, of the total length, but 

 draws it 31 per cent., or nearly a third. Another writer says that " the posterior fins touch the vesiculce seminales," 

 yet draws them far apart; in another species he describes the tail-segment as a fourth of the whole length, and 

 draws it as 35 per cent., or more than a third. "When one finds such inaccuracies in easily measurable matters, 

 absolutely no reliance can be placed on the figure as a whole. 



SECOND series. — ZOOLOGY, VOL. X. 10 



