14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



Subfamily Mononchinae. 



Genera: Mononchuhis Cobb, 1918; Mononchus Bastian, 1865 (sg. 

 Sporonchulus Cobb, 1917; sg. Pj-ionchuhis Cobb, 1916; sg.Mylonchnlus 

 Cobb, 1916; sg. Anatonchiis Cobb, 1916; sg. lotonchiis Cobb, 1916). 

 Subfamily Tripyloidlnae. 



Genera: Tripyloides de Man, 1886; Parachromagaster Allgen, 1929; 

 Cothonolaimus Ditlevsen, 1919 (syn. Macrolaimus Ditlevsen, 1919, 

 preocc.) ; Bathylaimus Cobb, 1893; Bathylaimella Allgen, 1930; 

 Halanonchus Cobb, 1920; f Rhabdocoma Cobb, 1920. 



KEY TO SUBFAMILIES OF TRILOBIDAE 



1. (2) Buccal capsule free, large, thick-walled; soil and fresh- 



water forms Mononchinae 



2. (i) Buccal capsule absent, or narrow, or if large never 



thick-walled, and if free then only to a small extent. 



3. (4) Amphids typical, pocketlike; spicular apparatus not 



complex ; fresh-water and soil forms Trilobinae 



4. (3) Amphids mostly atypical, either spiral-shaped or 



rounded (except Halanonchus) ; spicular apparatus 

 of a complex type, with a large gubernaculum ex- 

 ceeding the spicules in length; marine forms Tripyloidinae 



The preceding family, with only a very few exceptions, is com- 

 posed of marine forms; on the other hand, the remaining three 

 families contain mostly fresh-water and soil nematodes, with only 

 comparatively few members occurring in the sea. The Trilobidae, 

 while conserving some of the primitive features of the preceding 

 family, have completely lost the primitive wide attachment of the 

 esophagus to the cuticle of the head. In all its members the esopha- 

 gus is wide, of nearly the same diameter from the anterior end to 

 the cardia; the cardia is well developed, in some genera with typical 

 glandular cells inside; the caudal glands and the spinneret are 

 present in almost all genera. In the type genus, Trilohus, (fig. 17) 

 there is a broad mouth capsule with two denticles at its base. Tripyla 

 has a very similar mouth capsule with the same denticles, but it can 

 be closed, thus disappearing almX)st completely ; in such a closed posi- 

 tion only the straight contours of its walls anterior to the denticle 

 show the presence of firm, differentiated cuticle. In the preserved 

 specimens of that genus the cuticle is often distinctly striated, but this 

 striation is never apparent in living specimens, the cuticle in these 

 being perfectly smooth as in other members of the Enoplata; the 

 causes of this have never been investigated closely, but probably it is 

 due to some internal striation. In most of the genera there are a 

 larger number of preanal organs instead of one or two as in the Eno- 

 plidae. In some, such as Trilobus, they are highly differentiated; in 



