1911] Michael: Chactognaiha of the San Diego Eegion. 53 



long and slender, the width being about 4 per cent. Body slightly 

 widest between ventral ganglion and origin of lateral fins, tapering very 

 gradually forward and backward from this point. Neck evident. Con- 

 striction at tail-septum nearly absent. 



Lateral fin extends to seminal vesicles. More than 50 per cent of fin 

 behind tail-septum. The interval between anterior limit of fin and 

 ventral ganglion varies from 17 to 21 per cent. 



Vestibular ridge is apparently absent. Teeth 10 to 14 in the San 

 Diego specimens. Fowler (1905) records 7 to 13. Unlike E. pacifica, 

 the teeth (pi. 3, fig. 25) are not conspicuously bayonet-shaped. Seising 

 jaws (pi. 4, fig. 36), 7 to 9, very flat, broad, thin, and evenly curved. 

 The points are extremely fine and delicate. 



TABLE 15 

 Measurements of Eukrohnia subtilis'^ 



C Lateral fin X f 



1 All measurements made in per cent of total length of animal. 



2 Per cent of lateral fin in front of tail-septum. 



This species is readily distinguished from all other Chaetog- 

 natha except E. pacifica, to which it bears a remarkably strong 

 resemblance. The few points of difference are as follows. Teeth 

 of E. suhtilis not so conspicuously bayonet-shaped. Body thinner 

 for its length, and slightly more uniform in width. Seizing jaws 

 thinner and more uniformly curved. Whether these differences 

 are sufficient to distinguish two otherwise almost identical 

 species is doubtful but, owing to the scarcity of material, it is 

 impossible to make a positive statement regarding either their 

 identity or validity. 



