THE CILIATES 



359 



O. obtusuni (Dogiel and Fedorowa, 

 1925) (syn., Diplodinium hegneri Becker 

 and Talbott, 1927) measures 118 to 148 

 by 55 to 80 [i and has an ellipsoidal, only 

 slightly flattened body, with a smoothly 

 rounded posterior end. The posterior 

 part of the skeleton extends across only 

 2/3 of the upper side. The macronucleus 

 is elongate and rod-like. There are 6 

 contractile vacuoles. This species occurs 

 in the rumen of cattle and reindeer. 



O. venustum Kofoid and MacLennan, 

 1932 measures 76 to 115 by 41 to 60 (n and 

 has a triangular body with a small pos- 

 terior right lobe. The skeletal plate ex- 

 tends beneath the upper surface between 

 the macronucleus and the right side. The 

 macronucleus has 2 left lobes. There are 

 2 contractile vacuoles. This species oc- 

 curs in the rumen of the zebu. 



O. dogieli Kofoid and MacLennan, 

 1932 measures 92 to 130 by 48 to 63 (n and 

 has an ellipsoidal body with a strongly 

 convex left side, a slightly convex right 

 side and a flattened right lobe lying below 

 the cytopyge. The skeletal plate extends 

 between the macronucleus and the right 

 side. The macronucleus has 2 left lobes 

 (1 anterior and 1 median). There are 2 

 contractile vacuoles. This species oc- 

 curs in the rumen of the ox. 



O. clipeolum Kofoid and MacLennan, 

 1932 measures 92 to 128 by 50 to 65 fi arid 

 has an ellipsoidal body with a flattened 

 lobe projecting from the right posterior 

 surface below the midline. The skeletal 

 plate extends beneath the upper surface 

 between the macronucleus and the right 

 side. The macronucleus has 2 left lobes. 

 There are 3 contractile vacuoles. This 

 species occurs in the rumen of the zebu. 



O. monolobum Dogiel, 1927 meas- 

 ures 105 to 150 by 55 to 77 jx and has a 

 rectangular body with a large right lobe. 

 The skeletal plate extends under only 2/3 

 of the left side. The macronucleus is 

 elongate and rod-like. There are 5 con- 

 tractile vacuoles. This species occurs 

 in the rumen of the ox. 



O. dilobum Dogiel, 1927 measures 

 88 to 140 by 54 to 78 ^ and has an ellip- 



soidal body with a laterally flattened right 

 lobe and a flattened left lobe. The skeletal 

 plate extends under only 2/3 of the left side. 

 The macronucleus is elongate and rod- 

 like. There are 5 contractile vacuoles. 

 This species occurs in the rumen of cattle. 



O. rugoloricatiim Kofoid and Mac- 

 Lennan, 1932 measures 84 to 125 by 37 to 

 58 \i and has a rectangular body with a 

 flattened right lobe. The left side of the 

 exceptionally large skeletal plate turns in 

 and extends toward the middle of the body. 

 The macronucleus is straight and rod-like. 

 There are 3 contractile vacuoles. This 

 species occurs in the rumen of the zebu. 



Genus ENOPLOPLASTRON 

 Kofoid and MacLennan, 1932 



The metoral and adoral zones of mem- 

 branelles are near the anterior end. There 

 are 3 separate or partially fused skeletal 

 plates beneath the upper and right surfaces 

 of the body. There are 2 contractile vac- 

 uoles. The pharyngeal fibrils are heavy. 



Enoploplastron triloricatum (Dogiel, 

 1925) measures 60 to 112 by 37 to 70 ju, and 

 has an ellipsoidal body with a smoothly 

 rounded posterior end. The skeletal plates 

 are separate. The macronucleus has a 

 shallow depression in the anterior half of 

 its left side. This species occurs in the 

 rumen of the ox, reindeer and an African 

 antelope. 



RELATIONS OF RUMEN CILIATES 

 TO THEIR HOSTS 



Ciliates swarm in such tremendous 

 numbers in the rumen and reticulum that 

 everyone who has seen them has specu- 

 lated on their role in their host's nutrition. 

 This problem has been reviewed by Hungate 

 (1950, 1955) and Oxford (1955, 1955a), to 

 whose papers reference is made for fur- 

 ther details. It should be said that in 

 these reviews the name "Diplodinium'' is 

 used for practically all the ophryoscolecids 

 except Entodinium and Ophryoscolex, but 

 the other genera involved can often be de- 

 termined from their specific names. 



