ON ONCHNESOMA STEENSTRUPII. 235 
On Onchnesoma Steenstrupii. 
By 
Arthur E. Shipley, Mi.Ae, F.L.S., 
Fellow and Lecturer of Christ’s College, Cambridge, and Demonstrator of 
Comparative Anatomy in the University. 
With Plate IX. 
Tuer genus Onchnesoma was established in the year 1877 by 
Koren and Danielssen,! its name being derived from dyyvn =a 
pear, and cua =body. The genus is characterised as follows: 
.“ The body small, pear-shaped. The proboscis long. The 
anal aperture a little in front of the base of the proboscis. 
No tentacles; no vascular system. One retractor.” 
The genus consisted of two species: O. Steenstrupii, 
which the authors regard as synonymous with Sipunculus 
pyriformis of Danielssen? and Phascolosoma pusillum 
of Sars ;and O. Sarsii, synonymous with the Phascolosoma 
levissimum of Sars.3 These two species, with their charac- 
teristics, are mentioned in Selenka’s monograph of the Sipun- 
culide. In 1881 a third species, O. glaciale, was described 
by the Norwegian authors* from amongst the material col- 
lected by the Norwegian North Atlantic Expedition, so that 
1 “Contribution to the Natural History of the Norwegian Gephyrea,” by 
J. Koren and D. C. Danielssen, ‘Fauna Littoralis Norvegie,’ Bergen, 1877. 
2 Danielssen, ‘ Videnskabsselskabet Forhandlinger 1. Christiania,’ Aaret, 
1859. 
3 Sars, ‘ Videnskabsselskabet Forhandlinger i. Christiania,’ Aaret, 1868. 
4 ¢The Norwegian North Atlantic Expedition, 1876—1878, Gephyrea,’ by 
D. C. Danielssen and Johan Koren, Christiania, 1881. 
VOL, XXXIII, PART Il.—NEW SER. Q 
