On Onchnesoma Steenstrupii. 



By 



Arthur E. Sblpley, M.A,, F.Ii.S., 



Fellow and Lecturer of Christ's College, Cambridge, and Demonstrator of 

 Comparative Anatomy in the "University. 



With Plate XV. 



The genus Onchnesoma was established in the year 1877 by 

 Koran and Danielssen/ its name being derived from oyxvn =a 

 pear, and crCo/j.a =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 2 and Phascolosoma pusillum 

 of Sars ;^ and O. Sarsii, synonymous with the Phascolosoma 

 Isevissimum of Sars.^ These two species, with their charac- 

 teristicSj are mentioned in Selenka's monograph of the Sipun- 

 culidae. 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 



' "Contribution to the Natural History of the Norwegian Gephyrea," by 

 J. Koren and D. C. Danielssen, 'Fauna Littoralis Norvegise,' Bergen, 1877. 



^ Danielssen, ' Videnskabsselskabet Forhandlinger i. Christiania,' Aaret, 

 1859. 



^ Sars, ' Videnskabsselskabet Forhandlinger i. Christiania,' Aaret, 1868. ■ 



* 'The Norwegian North Atlantic Expedition, 1876—1878, Gephyrea,' by 

 D. C. Danielssen and Johan Koren, Christiania, 1881. 



VOL. V, PART II. 8 



