522 FRESH-WATER BIOLOGY 



7 (75) Esophagus prominent, muscular, with triradiate lumen. 



Suborder Myosyringata . . 8 



8(15) Bursa present in male and conspicuously developed 9 



9 (14) Male with broad bursa traversed by system of rays. Buccal cap- 



sule usually well developed in both sexes. 



Superfamily Strongyloidea Weinland 1858 . . 10 



With the spherical buccal capsule may easily be confused the bivalve oral armature of 

 some of the Spiruroidea. The former presents in cross-section an unbroken circle, or oval. 

 The latter is distinctly composed of two pieces interrupted along lines of division. In the 

 former the mouth opening is a ring that may be dentate or serrate but is still complete; in the 

 latter the mouth opening is a sUt having at opposite points two deep acute angles. A buccal 

 capsule is wanting in the three forms described here. 



The bursa in the strongyles is a conspicuous broad flaring organ, supported generally by 

 six paired rays and one unpaired median ray, all extending outwards from a common center 

 much hke the ribs of an imibrella. 



Only a very few strongyles have been reported in North America from aquatic hosts and these 

 few are not representative of the majority of the group to which belong the hookworms and 

 other well-known and abundant parasites of land animals. The three species cited here are in 

 truth so unlike typical strongyles that it is difficult to bring them into the key. 



Since the group is very large and complex and only three species are to be considered here 

 no effort has been made to outline the famihes or the numerous other subdivisions. The 

 key is merely a convenient way of separating these few species. It is not unlikely that other 

 genera are represented in the same and other aquatic hosts. 



10 (11) In reptiles and amphibians. . Strongylus auricularis Zeder 1800. 



No buccal capsule; 30 longitudinal ridges on the body. Spicules bifid or trifid at the distal ' 

 end. 



Reported by Leidy in 1856 from the intestine of Bufo americana, and Cistudo Carolina in 

 Philadelphia. No otherdata accompany the record so that it cannot be verified at present. 

 At least two species are included in European records imder this name. 



The genus Strongylus is grouped by RailUet and Henry under the family Strongylidae, sub- 

 family Strongylinae, tribe Stronglyeae. 



Ransom is uncertain as to the genus in which Zeder's or Schneider's species should be placed 

 but thinks they evidently belong in the family Trichostrongylidae. Probably Leidy's form 

 will fall in the same group. 



11 (10) In mammals 12 



12 (13) From frontal sinus of aquatic carnivore. 



Filaroides van Beneden 1858. 

 RaiUiet and Henry include this genus in the subfamily Metastrongylinae. 



Only species known . Filaroides mustelarum van Beneden 1858. 



No description of the North American form has been given as yet. Identified as European 

 species from host and effect. 

 -In frontal sinuses of various Mustelidae: skunk, weasel, mink, and otter, from northeastern 

 Jjforth America. Produces large asymmetrical postorbital swellings. 



13 {\2) From intestine of aquatic rodent. 



Trichostrongylus fiberius Barker and Noyes 1915. 



Capsule absent in both sexes. Male 2,8 mm. long, 0.013 

 to 0.09 mm. broad. Bursa with broad lateral lobes and 

 narrow dorsal lobe. Spicules short and heavy. 



Female 4.7 mm. long, 0.03 to 0.13s mm. broad. Vulva 

 near posterior end. Eggs oval, 0.059 by 0.036 mm., shell 

 thick. 



Intestine of muskrat. Nebraska. 



The genus Trichostrongylus is type of the subfamily Tri- 

 chostrongylinae. 



Fig. 815. Trichostrongylus fiberius. Posterior end of male. X 150. 

 (After Barker.) 



