20-5 



3i 



20.0 



3° 



19-0 



3 1 



i8-5 



3 2 



18.0 



32 



17.0 



29—30 



16.0 



3i 



15.0 



26—30 



14.0 



28-32 



13.0 



30 



1 2.0 



27 



n-5 



30 



[ 1.0 



27—36 



10. 



30 



closely set, very broad below. Posterior teeth long, strong, broad, closely set centrally but 

 diverging distally, abruptly pointed. The points of both sets of teeth very small. 



Vestibular ridge strongly and regularly mammillated, terminating externally in a very 

 blunt process. Corona ciliata very long, reaching up to three quarters of the distance to the 

 o-anglion, or even to close to the abdominal ganglion and anterior fins, commencing in front 

 of the eyes. Formulae: — 



6 8 14 



5 9 H 



5 § *3 

 5 — 6 7 — 8 11 — 12 



6812 



5 — 6 6- — 10 1 1- 



6 6 — 7 1 1- 

 5—6 7—9 11- 

 5—6 6—8 10- 

 5 — 6 8—9 12 — 14 

 5-6 7-8 11- 



5 6 IO 



6 7—8 1 1 



6 4—7 9— 11 



Specimens of 1 1 mm. and less are practically indistinguishable from the supposed robusta 

 in most cases. 



4. Sagitta hexaptera d'Orbigny. 



D'ORBIGNY. Voyage dans l'Amerique meridionale. Tome V, 3 m e Partie, Mollusques p. 140. 



Paris, 1835 — 1843, 4'°. 

 O. HERTWIG. Die Chaetognathen. Jenaische Zeitschrift, Band XIV, p. 196. 

 Sagitta magna Langerhans.- 

 P. LANGERHANS. Die Wurmfauna von Madeira, III. Zeitschrift fur wissenschaftliche Zoologie, 



XXXIV, p. 135. 

 ? Sagitta magna Grassi. 

 B. Grassi. Op. cit., p. n. 

 Sagitta tricuspidata Kent. 

 S. Kent. On a new species of Sagitta from the South Pacific. Annals and Magazine of 



Natural History, Series 4, Vol. V, p. 268. 

 L. DONCASTER. Op. cit., p. 2IO. 



Of these three "species", hexaptera, thanks to the careful monograph of Oscar Hertwig, 

 is as easily recognisable as any Chaetognath, although even he gave little detail of the variation 

 in the armature. The other two were most insufficiently characterised by their founders, though 

 a more detailed account, supposed to refer to magna, was furnished by Grassi. In general 

 appearance the three are stated to resemble each other closely, but to differ in their formulae 

 for jaws and teeth : 



