206 



PART II. SYSTEMATIC ACCOUNT 



Fig. 107. Siboglinum vinculatum: 

 Spermatophore (only the proximal 

 part of the filament is figured). 



free of sperm. The sperm are arranged paral- 

 lel to the axis of the spermatophore. The base 

 of the filament, springing from the rounded 

 end, is constricted, then swiftly expands into 

 a rather broad plate, which soon runs into the 

 ribbon-like basal part of the filament (Fig. 

 107). The spermatophores are about 0-3 mm 

 long and a little more than 0-02 mm broad. 



The stoutish, coarse tube consists of lack- 

 lustre white rings divided by narrow trans- 

 parent interspaces (Fig. 106АГ, L). The rings 

 are a little longer than broad, and in the front 

 part of the tube each ring is just perceptibly 

 constricted in the middle (Fig. 106AT). The 

 longer tube, that of the male, is 14-5 cm long, 

 but it is torn off at both ends. The tube of the 

 female, in two fragments, is 11-6 cm long. 

 This tube may be distinguished from the 

 slightly brownish tubes of S. cinctutum p. 

 207) and of S. frenigerum p. 213) by its 

 absolute whiteness. 



The major characteristic features of S. vin- 

 culatum are as follows: the possession of three 

 annular grooves between the base of the ten- 

 tacle and the bridle, the fusion of the dorsal 

 ends of the keels of the bridle, the arrange- 

 ment of the pinnules in two rows, the hig- 

 gledy-piggledy placing of the papillae of the 

 zone of thickening and their possession of 

 cuticular plaques, the absence from the 

 toothed platelets of any teeth pointing back- 

 wards, and the most characteristic shape of 

 the spermatophores. 



S. vinculatum is most closely related to S. 

 cinctutum, from which it may be disting- 

 uished by the pattern of secondary rings on 

 the fore part of the mesosoma, by the double 

 row of pinnules, and by the dorsal fusion 

 of the keels of the bridle. The peculiar 



