4 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 79 



rounding the mouth. Mouth cavity small. Cervical papillae 

 present or absent. Cuticle marked with 25 to 35 longitudinal ridges 

 appearing as simple lines, except under high magnification when 

 they sometimes show a finely beaded appearance. Cuticle of the 

 head may be slightly dilated, forming a narrow collar, or annulus. 

 Bursa with two lateral lobes united by a smaller median lobe and 

 each lateral lobe supplied with six supporting rays. The two ventral 

 rays usually approach each other near the margin of the bursa. The 

 tips of the medio-lateral, postero-lateral, and externo-dorsal rays are 

 in relation with the posterior border of the bursa. The dorsal ray 

 separates into two main branches, which may divide distally into 

 two short branches or give off one or two short side branches in- 

 ternally or externally. There is an accessory bursal membrane sup- 

 ported by two slender diverging rays. The spicules are short (less 

 than 1 mm. long), similar in size and shape. They may be undivided, 

 bifurcate, or trifurcate in their distal portions. A gubernaculum 

 may be present or absent. Prebursal papillae are present. Vulva 

 is less than one-fifth the length of the body from the posterior end, 

 naked or covered by a thin, backward-projecting, cuticular flap. 

 Ovejectors are well developed. Eggs, oval, with thin shells. 



Tyfe species. — Ostertagia ostertagi (Stiles, 1892), Ransom, 1907. 



KEY TO THE SPECIES OF OSTEKTAGIA RANSOM. 1907 



\. Spicule structure not ascertainable Group D 



Spicule structure ascertainable II 



II. Spicules undivided Group A 



Spicules divided III 



III. Spicules bifurcated Group B 



Spicules trifurcated Group O 



GROUP A.— SPICULES UNDIVIDED 



1. Dorsal ray more than 100m long ; gubernaculum trihedral in shape bullosa 



Dorsal ray less than 100/u long 2 



2. Gubernaculum present asymmetrica 



Gubernaculum absent houdemeri 



GROUP B. SPICULES BIFURCATED 



1. Spicules 700m long mentulata 



Spicules less than TOO/u long 2 



2. Spicules more than 400m long turkestanica 



Spicules less than 400m long 3 



3. Dor.sal rays originating from a common trunk khalili 



Dorsal rays not originating from a common trunk circumcincta 



GROUP C. SPICULES TRIFURCATED 



1. Distal portion of spicule divided into two ventral pi'ocesses and 



one dorsal process 3 



Distal portion of spicule not so divided 2 



