A NEW NE^IATODE, OSTERTAGIA BULLOSA, PARASITIC 

 IN THE ALIMENTARY TRACT OF SHEEP. 



By Brayton Howard Ransom, 



Assistant Custodian, Helminthological Collections, United States National Museum, 



AND 



^Iaurice C. Hall, 



Assistant Zoologist, Bureau of Animal Industry, United States Department of Agriculture. 



The nematode described in this paper was first collected by the 

 junior author at an abattoir in Colorado Springs, Colorado, April 28, 

 1911. Comparison with the descriptions of species given in Ransom 

 (1911) led to the conclusion that the species was probably new. 

 Specimens were then sent to the senior author who also was of the 

 opinion that it was a new species. The sheep from which this ma- 

 terial was collected were originally from the ranch of Mr. W. II. WeUs 

 near Resolis, Colorado, and specimens of the nematode here described 

 were collected by both of us during the summer of 1911 from sheep at 

 Mr. Wells's ranch. The nematode was found in nearly every sheep 

 examined at the ranch and was the only nematode found in the 

 stomach with the exception of the stomach worm, Hxmonchus con- 

 tortiLs. The new species was also found by us in sheep at the ranch 

 of Mr. W, T. Kennedy near Amo, Colorado. A single specimen was 

 found once in the intestine, but the occurrence of this nematode in the 

 intestine was probably accidental, as the fourth stomach is evidently 

 the normal location. In Colorado the greatest number of Ostertagia 

 found in a single sheep was 73 and the greatest number of Hsemonchus 

 contortus, 537. Usually there were less than a dozen of each. This 

 comparative freedom from infection wdth nematodes in Colorado 

 sheep is to be attributed in part to the dry cUmate and in part to the 

 extensive area covered in range feeding, thereby preventing concen- 

 tration of infection. 



Mr. W. D. Foster of the Zoological Division, Bureau of Animal 

 Industry, has called our attention to a single specimen of a nematode, 

 a female, collected by him May 13, 1910, from a sheep received in 



Proceedings U. S. National Museum, Vol. 42— No. 1892. 



175 



