1911] Michael : Chaetognatha of the San Diego Region. 51 



Apparently, we have but two fairly sure characters for dis- 

 tinguishing between S. neglecta and 8. regular is. One consists 

 in the per cent of posterior fin in front of tail-septum, which is 

 33 in S. regularis and never less than 38 in S. neglecta. The 

 other point of difference consists in the width, and especially 

 the length of collarette as defined above. Perhaps we have here 

 the exphination of the more uniform width of body in »S*. regu- 

 laris. 



S. neglecta also bears considerable resemblance to S. 

 hipunctata. The following differences, however, exist. In the 

 latter species the anterior fins never reach the ventral ganglion, 

 there is more instead of less than 50 per cent of posterior fin in 

 front of tail-septum, and the general appearance is much more 

 transparent. 



Genus Eukrohnia Ritter-Zahony 



Syn. Krohnia Laiigerhans 



Eukrohnia hamata (Mobius) 



PI. 2, fig. 8; pi. 4, fig. 35. 



EulTohnia hamata, Ritter-Zahony (1909c), p. 792, (1910), p. 268. 

 Sagitta hamata Mobius (1875), p. 158. 

 Spadella hamata, Hertwig (1880), p. 73. 



Krohnia hamata, Langerhans (1880), p. 136; Krunibach (1903), p. 

 639; Strodtmann (1892), p. 20; Fowler (1905), p. 74, (1906), 

 p. 23. 

 Krohnia foliarea Aida (1897), p. 19. 



Cliaracters 



Body firm and opaque (pi. 2, fig. 8) as in S. serratodentata. Neck well 

 marked. Body thickest throughout middle third, tapering gradually 

 toward head and tail. Muscles heavy and thick. Slight constriction 

 at tail-septum. 



Lateral fins long, extending from ventral ganglion to some distance 

 behind tail-sejitum. They never extend more than half way from tail- 

 septum to seminal vesicles. Widest near plane of tail-septum, sometimes 

 slightly in front and sometimes slightly behind. As described by Fowler 

 (1905), the absence of fin rays seems to be characteristic. 



Vestibular ridge apparently absent. According to Fowler (1906, p. 

 23) there "exists a very slight ridge with sense bulbs in the position 

 •of the vestibular ridge in Sagitta." In the San Diego specimens I have 

 been unable to determine this with certainty. 



Teeth 10 to 13 in the San Diego specimens. This agrees more nearly 

 with Fowler's (1905) variety of E. hamata than with the usual species, 

 which bears from 16 to 22. 



