NO. 6 CLASSIFICATION OF NEMATODES FILIPJEV I9 



ania de Man, 1876; Dintheria de Man, 1922; Deontolaimus de Man, 1880; 

 Leptolaimus de Man, 1876; Conolaimella AUgen, 1930; Antomicron Cobb, 

 1920; Cynura Cobb, 1920; P olylaimium Cobb, 1920. 



This family should be regarded as the most primitive one in the 

 order. The cuticle is somewhat thickened around the mouth open- 

 ing, and the esophagus is attached to this thickening by a narrow 

 strip (fig. 27), this simple arrangement being realized in all genera 

 without any complications. The amphids are mostly spiral-shaped 

 and in a forward position. Most of the genera are marine, but some 

 are fresh-water, rarely soil, nematodes. 



Dermatolaimus is one of the simplest members of the family 

 (fig. 28). It is the single member of the order with a more or less 

 extensive attachment of the esophagus to the cuticle ; this is possibly 

 due to the reduction of the musculature in the anterior part of the 

 former. There is no differentiation in the mouth structures. The 

 latter are complicated in Caniacolaimns and in some other genera by 

 the formation of spears that seem to be protrusible. In the fresh- 

 water genus Aphanolaimus there is a complete absence of differen- 

 tiated mouth structures ; the amphids are rounded with a bubblelike 

 median swelling (figs. 29, 30). The closely related Paraphanolaimus 

 has typical spiral amphids. In young specimens of Aphanolaimus 

 the writer has seen on the larval skin a true spiral amphid and a 

 typical swollen one under it. The preanal tubes are peculiar to that 

 genus and are vei^ similar to that of some species of Plectus, thus 

 giving a connecting link to the following family. 



Genera of the Family Plectidae 

 Genera: Plectus Bastian, 1865; Pycnolaimiis Cobb, 1920; Haliplectus Cobb, 

 1913; Wilsonenia Cobb, 1913; Anthonema Cobb, 1906; Aulolainioides 

 Micoletzky, 1917; Chronogaster Cobb, 1913; Paraplectus Filipjev, 1929; 

 Rhahdolaimiis de Man, 1880; Isolaimium Cobb, 1920; Tripyliuin Cobb, 

 1920; IValcherenia de Man, 1922c; Pseudobathylaimus Filipjev, 1918 (syn. 

 Bathylainms Daday, 1905, preocc. ; syn. Dadaya Micoletzky, 1922) ; Para- 

 doxolaimus Kreis, 1924; Pseiidochromadora Daday, 1900; Aplectus Cobb, 

 1914; Diodontolaimus Southern, 1914. 



This family, like the foregoing one, has irreversible mouth 

 organs, but the circumoral thickening of the cuticle is not so pro- 

 nounced. The difference between the two is in the complication of 

 the inner esophageal tube ; this is simple in the Camacolaimidae, but 

 in the Plectidae it forms ordinarily a well-isolated buccal capsule an- 

 teriorly, followed by a valvular constriction, and with a dilatation 

 inside the well-developed bulbus, with or without masticatory plates. 



