1912-13.J Hydroids of British Antarctic Expedition, 1908. 33 
my measurements (see table above) indicate that the proportion free is even 
greater — rather over three-fourths. Lastly, in Sertularella plectilis the 
embayments between the teeth on the margin of a hydrotheca are much 
deeper, and the teeth therefore appear much longer and more pointed than 
do those of Sertularella glacialis (cf. figs. 10 and 11). These points, at 
least in the aggregate, definitely separate the two species concerned. 
GUIDE TO LITERATURE CITED. 
Allman, 1872 : A Monograph of the Gymnoblastic or Tubularian Hydroids , pt. ii. 
Ray Society, London. 
Allman, 1877 : “Report on the Hydroida (Gulf Stream Explor.),” Mem. Mus. 
Comp. Zool. Harvard , vol. v. 
Allman, 1888 : “ Report on the Hydroida,” ii., Rep. Sc. Res. “ Challenger ,” Zool., 
vol. xxiii. 
Billard, 1906 : “Hydroides,” Exp. Antarctique Frangaise (1903-1905 ), Sc. nat. 
Paris. 
Billard, 1907 : “Hydroides,” Exp. sc. “ Travailleur ” et “ Talisman ,” t. viii. 
Billard, 1910 : “Revision d’une partie de la collection des Hydroides du British 
Museum,” Ann. Sc. Nat. (N.S.), t. xi. Paris. 
Broch, 1909 : “Die Hydroiden der arktischen Meere,” Fauna Arctica. Jena. 
Ehrenberg, 1834: “Beitrage zur physiologischen Kenntnis der Corallentiere ini 
Allgemeinen,” etc., Abh. K. Ahad. Wissens. Berlin. 
Hartlaub, 1904 : “ Hydroiden,” Resultats du voyage du S.Y. “ Belgica ” en 1897 , 
1898, 1899. Anvers. 
Hartlaub, 1905 : “ Die Hydroiden der magalhaensischen Region und chilenischen 
Kliste,” Zool. Jahrb., Suppl. vi., “Fauna Chilensis.” 
Hartlaub, 1900: “ Revision der Sertularella- Arten,” Abh. naturw. Ver. Hamburg, 
Bd. xvi. 
Hickson and Gravely, 1907 : “ Hydroid Zoophytes,” National Antarctic Expedi- 
tion, Natural History, vol. iii. British Museum. 
Hincks, 1861 : “A Catalogue of the Zoophytes of South Devon and South 
Cornwall,” Ann. Mag. Nat. Hist. (3), vol. viii. 
Hincks, 1868 : A History of the British Hydroid Zoophytes. London. 
Jaderholm, 1904: “ Mitteilungen liber einige von der schwedischen Antarctic- 
Expedition 1901-1903 eingesammelte,” Arch. Zool. exp. et gen. (4), t. iii. 
Jaderholm, 1905 : “ Hydroiden aus antarktischen und subantarktischen Meeren, ’ 
Wissens , Ergeb. schwedischen Sudpolar-Expedition 1901-1903, Bd. v, Lief. 8. 
Jaderholm, 1909: “ Northern and Arctic Invertebrates in the Collection of the 
Swedish State Museum : iv., Hydroiden,” Kungl. Svenslca Vetenslcapsak. Handl., 
Bd. xlv. 
Kirchenpauer, 1884: “Nordische Gattungen und Arten von Sertulariden,” 
Abh. naturw. Ver. Hamburg, Bd. vi. 
Kramp, 1911 : “Report on the Hydroids, ’’Danmark Ehspeditionen til Gronlands 
Nordostkyst 1906-1909 , Bd. v. No. 7. Kopenhavn. 
VOL. XXXIII. 
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