DESMODORINAE 135 



Cviticle finely striated, without bristles except in the 

 cervical region. Head not distinct, but narrowed, with two 

 crowns of bristles and covered by a specialized cuticular cap. 

 Pharynx short, three-sided, containing a dorsal tooth which 

 may be simple or bilobed. Oesophagus without bulb, but 

 with ocelli, which may be furnished with lenses. Caudal end 

 of male with several pairs of ventral preanal and postanal 

 bristles. There may be a single median preanal supplementary 

 organ and two rows of submedian supplementary organs. A 

 bipartite accessory piece present. Testes opposed, out- 

 stretched. Female genital tubes paired, opposed, reflexed. 

 Caudal glands and spinneret present. 



Hab. Marine. 



Genotype : probably T. echinodon Marion, 1870, according 

 to Stiles & Hassall (1905). 



Marion, 1870, An7i. Sci. Nat., Paris, Zool., xiii, 25; Cobb, 

 1914, Contr. Sci. Nematol, i, 31 ; de Man, 1904, Res. Voij. 

 S.Y. Belgica (Zool.), 25. 



The genus Hemvpsilus was considered by Biitschli (1874, 

 Abh. Senckenb. Ges., Frankfurt a. M., ix, 277) to be 

 a synonym of Thoracostoma. The original diagnosis (de 

 Quatrefages, 1864, Ann. Sci. Nat., Paris, Zool., (3) vi, 131) 

 and the description of his unnamed species are so incomplete 

 that we have decided to follow Biitschli, although it is doubt- 

 ful whether the genus could ever be recognized. The genus 

 Jdgerskioldia Filipjev, 1916, appears to have been proposed 

 for certain " sharp-tailed " species of Thoracostoma, including 

 T. acuticaudatum J agerskiold, 1901, which is probably intended 

 as its type. Deontostoma Filipjev was proposed for Thoraco- 

 stoma arcticum Savelev. The description of this species 

 (Savelev, 1912, Trav. Soc. Nat., Petrograd, xliii, 124) does 

 not, in our view, indicate any characters of sufficient import- 

 ance to justify the erection of a separate genus for it. Lepto- 

 somatides, according to Filipjev (1918, Trav. Lab. Zool., Stat. 

 Biol. Sebastopol, Ser. II, No. 4, 50), is intermediate between 

 Leptosomatum and Deontostoma. Leptosomatiini, in our view, 

 belongs to the family Alaimidae, and has no close relationship 

 to Thoracostoma. Leptosomatides, however, appears to differ 

 from typical species of Thoracostoma almost solely in the less 

 well-developed condition of its cephalic cuticular cap. We 

 have therefore included it in the synonymy of this genus. 



18. Thoracostomopsis Ditlevsen, 1919. 



According to Ditlevsen, this genus differs from Thoracostoma 

 in having the head much narrower than the rest of the body, 

 and also in the presence within the pharynx of a thin, acute 

 " spear " which may protrude from the mouth-opening. 



