194 FILTER-BED NEMAS 



fauna and flora of filter-bed sand may be made a criterion of the rate 

 and nature of the filtration. 



The general appearance of the sand in any particular part of the bed is 

 a clue to the rate and nature of the filtration there, but this rough method 

 is capable of refinement through the aid of a biological census. The 

 difficulty is we do not yet know what significance to attach to the 

 presence or absence of particular species. Should an attempt be made 

 to devise and apply such a method, it might be found that the presence 

 or absence of a few species would constitute a sufficient test. 



PARTIAL LIST OF THE NEMAS FROM AMERICAN SLOW SAND 

 FILTER-BEDS* 



Achromadora minima Cobb Washington, D. C. Mononchulus ventralis n. g., n. sp. 



Actinolaimus radiatus Cobb... .Washington, D. C. Washington, D. C. 



Aphanolaimus ? Philadelphia Mononchus longicaudatus Cobb 



Apheltnchus ep Pittsburg Washington, D. C. 



Atylenchus sp New Bedford ,, , ,.. . . ,. 



Cephalobustp Philadelphia Mon h * Philadelplua 



Cylindrolaimus obtusus Cobb... Washington, D. C. Plectus clrratus Bastian Washington, D. C. 



Dorylaimus fecundus Cobb Washington, D. C. Prismatolaimus sp Philadelphia 



Dorylaimus sp Washington, D. C. Rkabditis sp Philadelphia 



Dorylaimus sp Philadelphia Rhabdolaimus sp Washington, D. C. 



Dorylaimun sp Philadelphia Spilophora sp Harrisburg 



Dorylaimus Bp Washington, D. C. Teratocephalus sp Pittsburg 



lota simile n. sp Washington, D. C. Trilobus longus Leidy Philadelphia. 



Ironus americanus Cobb Philadelphia THpyla monohystera de A/ an ... Washington, D. C. 



Ironus ionavus Bastian Washington. D. C. Tylencholaimus sp ^^ Bethlehem, 



Ironus longicaudatus de M an. . .Washington, D. C. p. , 



Monhystera subfiliformis n. sp . .Washington, D. C. 



Monhystera dispar Bastian Washington, D. C. Tylenchus filiformu Butschh (?) 



Monhystera sp Philadelphia Washington, D. C. 



Monhystrella plectoides n. subg., n. ep. Tylenchus sp Philadelplua 



Washington, D. C. Xiphinema americanum Cobb Philadelphia 



* The larger number of species from the Washington beds is due to the examination of a larger num- 

 ber of samples than from beds elsewhere. The more important of these species are described below. 

 The drawings are from nature and were made under the author's personal supervision by Mr. W. E. 

 Chambers. 



MONONCHUS Bastian 1865 



1. Mononchus longicaudatus Cobb (See p. 161). The feeding habits of Monon- 

 chus are distinctly different from those of either of its frequent companions, 

 Tripyla and Ironus. In capturing food Mononchus depends largely upon the 

 grip of its powerful jaws. Tripyla depends upon its agility and its flexibility, 

 and possibly coils itself about its victim, after the manner of a boa constrictor. 

 Mononchus and Tripyla bolt their food, but Ironus feeds in an entirely different 

 way; attaching its lips to its food, it rips a hole in the external layers by the 

 outward stroke of its three, extremely sharp, radially acting onchi. As these 

 move forward their points move outward, and two or three such movements serve 

 partially to imbed the head of the Ironus. It would appear that then the more 

 or less fluid parts only are imbibed, for the contents of the intestine of Ironus 

 hardly ever present optically identifiable substances. It is manifest, however, 

 that the contents of the intestine are animal in character, and so it seems beyond 

 reasonable question that Ironus is carnivorous. I have never found the con- 

 tents of the intestine to respond to the starch test. 



