CHAETOGlSrATHA COLLECTED BY STEAMER ALBATROSS. 259 



SAGITTA FEROX Doncaster. 



Plate 35, fig. 7; plate 37, figs. 21, 25. 



Sagittaferox Doncaster (1902), p. 212.— Fowler (1906), p. 10.— Michael (1911), 



p. 74. 

 Sagitta robusta (part) Ritter-Zahony (1909a), p. 49; (1911), p. 16. 



Ritter-Zahony (1909a, 1911) synonymises this species to S. ro- 

 busta Doncaster and says (1909a, p. 49): "Ich glaube daher nicht 

 fehlzugehen, wenn ich niich fur die schon von Doncaster (1902, 

 p. 212) als moglich hingestellte Identitat dieser beiden Arten auspreche 

 und S.ferox nur eine altere S. robusta auffasse." Yet, although the 

 two species closely resemble each other, the Philippine specimens 

 do not indicate the slightest convergence with age in three important 

 differential characters (see Table 14): 



1 . The collarette is much wider in S.ferox and nearly always extends 

 beyond the anterior end of the ventral ganglion, while in S. robusta 

 it never extends much over halfway from neck to ventral ganglion. 



2. Anterior fins always extend beyond posterior end of ventral 

 ganglion in S. ferox, while in S. robusta there is an interval between 

 the fins and ganglion. 



3. Anterior fins are longer than posterior fins in S.ferox, while the 

 posterior fins are the longer in S. robusta. 



These three persistent differences justify considering S. ferox 

 valid until critical study of variations in these particulars can be 

 made. The species is therefore redescribed from the Philippine 

 specimens in hopes that this description may aid in establishing 

 its valid or synonymical position: 



Collarette (pi. 35, fig. 7) long and broad, extending past anterior 

 end of ventral ganglion onto anterior fins. Head large. Lateral 

 fields small. Body firm, opaque, and nearly of uniform width from 

 in front of ventral ganglion to tail-septum. Tail 25 to 30 per cent 

 of total length of animal. Corona ciliata not observed. 



Anterior fins (pi. 35, fig. 7) longer and slightly narrower than 

 posterior fins, always extending anteriorly beyond posterior end of 

 ventral ganglion, frequently past its middle and occasionally to its 

 anterior end. Form acutely triangular, the position of greatest 

 width being in posterior quarter of fin. 



Posterior fins (pi. 35, fig. 7) extend caudally to seminal vesicles. 

 Interval from anterior to posterior fins 3 to 7, usually about 5 per 

 cent of total length of animal. Less than 50 per cent (41 to 44) of 

 fin in front of tail-septum. Triangular in form, the position of 

 greatest width being about midway between tail-septum and seminal 

 vesicles. 



Vestibular ridge (pi. 37, fig. 21) strongly mamillated, the number 

 of papillae corresponding to the number of teeth. Wing of ridge 

 covers all except the first two teeth, the notch extending beyond 

 the fourth or fifth. External process short, broad, and blunt. 



