[450] 
= 
A synopsis of the northern and arctic species of the genus Phascolosoma. 
Group I. Retractor-muscles 4; separate, two dorsal and two ventral: 
Subdivision 1. Hooket present: 
Skin with papille at the posterior extremity of 
the body and at the base of the proboscis. 
Hooks irregularly arranged . 1. vulgare BLAINV. 
Skin bright, smooth, devoid of true apillg 
Hooks forming distinet rings 2. elongatum KEF. 
Subdivision 2. Hooks absent:. fö margaritaceum SARS. 
14. Hansemi DAN. and KOR. 
l3. Trybomi n.(?) 
Group II. Retractor-muscles 2; ventral, separate or not, 
not seldom united to a greater or smaller extent, 
always embracing the nerve-cord with their roots. 
Subdivision 3. Contractile vessel with numerous 
side branches. Tentacles 28—40. Hooks absent. 
Retractors separate, and their bases near the 
posterior extremity of the body. Skin wrinkled 
in fine zigzag lines with minute scattered papille 6. procerum MÖBIUS. 
Subdivision 4. Contractile vessel unbranched. Skin 
somewhat rough, lighter or darker greenish brown, 
not transparent, furnished with traces of meru- 
stations and with distinet brownish papille. Ten- 
tacles 27—40, normal, distinet. Hooks absent. 
Retractors separate =. . . «oc 7. eremila M, SARS. 
Subdivision 3. Vessel dör aneleder. missing. Skin 
smooth, bright, more or less hyaline or transpar- 
ent with no or very inconsiderable papille". 
Tentacles either still discernible, small, 83—24, or 
! Except Phascolosoma improvisum, which possibly is the male of Ph. Sabellarie. Op. the description 
of the species and »Does a sexual dimorphism exist among the Sipunculids?» at the beginning of this paper! 
