l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



laimellus Cobb, 1913 ; sg. Axonchiimi Cobb, 1920) ; Doryllium Cobb, 

 1920; Aciinolaimus Cobb, 1913. 



KEY TO SUBFAMILIES OF DORYLAIMIDAE 



1. (2) Buccal capsule completely toothless or absent Alaiminae 



2. (i) Teeth or spear present. 



3. (4) Three labial teeth present Ironinae 



4. (3) A buccal spear present, simple or triple, rarely sep- 



arated into three isolated rods. 



5. (6) Spear triple, in Diphfherophora separated into three 



rods Tylencholaiminae 



6- (5) Spear simple, short or elongated Dorylaiminae 



The most characteristic feature of members of this family is 

 their esophagus (fig. 20) ; it is narrow and the musculature is very 

 weak or even quite absent anteriorly, but gradually expanded and 

 normally formed posteriorly. Cobb had good reason to speak of a 

 " dorylaimoid " esophagus. The sensory organs of the head are 

 always in the form of papillae, a feature which is probably correlated 

 with their sucking habits, as in Mononchus. The caudal glands and 

 pore are absent in the fresh-water genera but present in the marine 

 ones. 



The first subfamily has no differentiated mouth structures. 

 Whether this is a primitive feature or should be considered as a ter- 

 minal stage in their reduction from previous structures is problem- 

 atical. The second possibility seems to me more probable because of 

 the general appearance of degeneration of the esophagus in some of 

 them. The Alaiminae, with their typical dorylaimoid esophagus, 

 might have arisen from some of the Dorylaiminae that had lost their 

 spear. It is possible that the investigation of the larval stages will 

 throw more light on this matter. 



The characteristic feature of the Ironinae is the presence of three 

 teeth immediately behind the lips. These teeth belong to the esoph- 

 agus. In the larvae they are formed before each molt in a position 

 posterior to the functional ones, moving forward in the course of 

 the molts. The teeth can be everted outside the mouth, functioning 

 as digging organs (Cobb, 1928). 



The Tylencholaiminae and Dorylaiminae are characterized by the 

 presence of protrusible spears. In the first subfamily there is a 

 threefold spear (fig. 21) arising from the three esophageal sectors. 

 In Dorylaiminae there is only one spear, subventral and asymmetri- 

 cal in position. In Nygolaimus it is distinctly separate from the 

 esophageal cuticle and simply acute (fig. 22). In Dorylaimus it has 



