380 University of California Publications in Zoology. [VOL. 6 



The shape of the spines may vary somewhat in different regions 

 of the same animal. Furthermore, all the spines thus far de- 

 scribed correspond exactly to those figured by Lonnberg, with 

 the exception of Spencer's figure of the spines of G. rugosa. 

 Possibly a study of more individuals of the latter species may 

 show closer similarity to the type of the genus. 



10. Size of eggs. This character must be regarded with some 

 distrust, in view of the fact that one individual may yield ripe 

 eggs varying in size from 0.075 mm. to 0.115 mm. 



11. Presence of an operculum in the egg-shell. Haswell 

 (1902) figures an egg of G. nigrosetosa, having a thick shell, 

 with a thin plate at one pole, in diameter less than one-third the 

 greatest transverse diameter of the egg (see my plate 47, figure 

 81.) "A circular area of the shell at one pole is much thinner 

 than the rest, and is probably differentiated as an operculum." 

 The same observer studied eggs of G. rugosa, and states that in 

 them the shell does not appear to be provided with an operculum. 

 The eggs of G. fimbriata show when discharged no such thin plate ; 

 but eggs taken from poorly preserved specimens show an oper- 

 culum, its diameter a little more than half the greatest transverse 

 diameter of the egg, in which the shell is slightly thinner than 

 elsewhere. Its margin is serrated. This cap differs in size, 

 thickness, and character of margin from the operculum of Has- 

 well, but seems to be an homologous structure. The significant 

 point is that there is no trace of it in the freshly discharged ova, 

 and that it does appear very clearly later. Probably the ova 

 of G. urna and G. rugosa would also show a similar structure, 

 at a similar stage. The problem is whether Haswell's oper- 

 culum is present in a freshly discharged or intra-uterine egg, or 

 whether it is merely an early stage of the formation of this cap. 

 Only in the former case does the operculum become a good 

 specific character. Haswell explicitly observes that "the speci- 

 mens were not in good condition for minute investigation." His 

 figure (see my plate 47, figure 80) shows the neck of the rosette 

 as swollen, recalling an appearance characteristic of worms kept 

 too long in culture media. But in the absence of any definite 

 statement as to the condition of the two specimens of G. nigro- 



