1911] Michael: Chaetognatha of the San Diego Region. 39 



as the fins were too damaged for description, it seems best to 

 have it remain a valid species until redeseription is possible. 



Sagitta serratodentata Krohn 



PI. 1, fig. 4; pi. 3, fig. 20; pi. 4, fig. 30; pi. 5, fig. 41. 



Sagitta serratodentata Krohn (1853), fig. 2; Hertwig (1880), p. 

 64; Strodtmann (1892), p. 17; Krumbach (1903), p. 636; Fow- 

 ler (1905), p. 58; Eitter-Zahony (1908), p. 15 (1909b), p. 8. 



Sagitta sp. ituiom., Gegenbaur (1856), p. 15. 



Sagitta gegenbauri Fol (1879), p. 123. 



General Appearance 



This slender, pin-shaped species, when placed upon a black 

 background, appears very opaque (pi. 1, fig. 4). The head, 

 ventral ganglion, intestine, and seminal vesicles are readily 

 distinguished as slightly more opaque than the body proper. 

 The seminal vesicles, when fully ripe, stand out clearly as 

 extremely opaque areas. The tail is slightly more transparent 

 than the body. The tail-fin and both pairs of lateral fins, in 

 perfectly preserved material, are barely visible to the naked eye, 

 appearing as nearly transparent areas. The ovaries, owing to 

 the opacity of the body, are very indistinctly seen. It is to be 

 noted that, wiien sexually mature (pi. 5, fig. 41) ^S. serratoden- 

 tata presents a much greater opacity, owing probably to the 

 greater length and opacity of the ovaries. When not mature 

 this species is slightly less opaque than 8. planktonis, but when 

 fully developed it is more opaque. 



•Characters 



Body firm and rigid, retaining its form well. Neck very prominent. 

 Body widest at abont middle of length, varying from 50 to 55 per cent, 

 and tapering very gradually toward head and tail. Lateral fields small. 

 Muscles broad and strong. No constriction at tail-septum. Collarette 

 absent. 



Anterior fin shorter and somewhat narrower than posterior fin. 

 Extends to ventral ganglion. Position of greatest width well toward 

 posterior end. Form approximately triangular. 



Posterior fin extends caudally to seminal vesicles when they are tumid. 

 In exception to all the other San Diego species, the proportion of posterior 

 fin in front of tail-septum is exceedingly variable, there being some- 

 times more and sometimes less than 50 per cent. Position of greatest 

 width well behind septum, usually at a point about half the distance to 

 .seminal vesicles. Interval from anterior to posterior fin small. 



Vestibular ridge (pi. 3, fig. 20) well developed, as long as posterior 



