74 THÉEL, NORTHERN AND ARCTIC INVERTEBRATES. I. SIPUNCULIDS. 
Number of — Length of | Diameter of | 
tentacles the body the body 
SPItZ borg OD gg bsr Li ake re RES SE IE 16 17 mm. 2.2 mm. Mossel Bay. | 
> BTR ORGNNON eko do INS 0 0: 20 30 mm. | -3.3 mm. | » | 
låsas! SR Her" DPA TRE | 21 20 mm. 4 mm. | Bel Sound. | 
» SSK Ol 1 SOK TEA SE eb eg rer ve åa 27 37 mm. 5 mm. | » | 
> ks bal SER EN FS LAS ol 29 35 mm. 5.2 mm. | | » | 
> a OVAT SE arg ÄRR AR ENA 32 | 31 mm. 5.3 mm. | Mossel Bay. | 
» RAN REN SAAEENERE, ÄRAN AA 37 34 mm. 5.5 mm. | Bel Sound. | 
Tinm ark ony sd E SOEA 27 | 35 mm. 3.7 mim. Locality ? | 
» NY. ÖT äl FN SG SE få DDT AG FED IGN BAG 31 28 mm. 3.5 mm. | » | 
I2atdsvi kor ISO bög Nov vv ob I O-00 C I 31 18 mm. 4.5 mm. | » | 
» NOT SA NRNG SKOR SAD 40 | 18 mm. 5.5 mm. » | 
NNK g 30 IC td ed BROR Oron Or OL FORD | 20 24 mm. 3.8 mm. | Nova Zembla. | 
» oå OMO SDJLDEr TD SI LO RDR Ord 010 0 KO I SEA 26 | 30 num. 4 mm. | Cape Golovin. | 
General Remarks on the "abyssorum-section'".' 
In this "section" are comprehended all those northern forms of Phascolosoma, 
which are comprised under the names of Ph. abyssorum, Lilljeborgii, Sabellarie, im- 
provisum, anceps, glaciale and Sarsi; the two latter were previously referred to the 
genus Onchnesoma of KOREN and DANIELSSEN. Any investigator who has had the 
opportunity of studying these forms, must perceive that the seven species in question 
really constitute one natural group of the Phascolosoma-genus. 
They have all a narrow, cylindrical trunk with a lustrous, almost smooth sur- 
face (except Ph. improvisum). In most cases their tentacles are reduced to an irre- 
gularly buckled or folded disk round the mouth. They are all in possession of two 
ventral retractors, which in most cases have grown together, so that they seemingly 
present themselves as a single retractor, with two larger or shorter roots, one on 
each side of the nervous cord: the roots are attached to the middle of the body or 
behind it, but never to the posterior extremity of the body. 
In consideration of the great conformity existing among several of the forms 
enumerated, there may arise the question as to whether they all are true separate 
species or not. In order to avoid confusion, I prefer to keep them separate for the 
present, because, according to my opinion, it is easy enough to join several forms, 
previously considered as distinct, to one species, while, on the other hand, it meets 
with great difficulty to sift out and define new species which have hitherto been 
confounded and lumped together with other forms in one species. But the conditions 
1! As I have been able to study large numbers of samples of Ph. Sabellarie and improvisum, the »ge- 
neral remarks» here given are mainly based on them, taking it for granted that they may be applicable to 
at least several other nearly related forms, 
