NEW FACTS CONCERNING BOTHRIOLEPIS. I1Q 



sagittal sections it is seen to be deeply concave on its median pos- 

 terior face, Fig. 4, A, mx. 



The lateral arm of the maxilla is a narrow band, dull black 

 and smooth. In the position shown in Fig. 3, it lies below the 

 oral membrane with its concave surface directed upward and 

 forward. 



At the union of the two arms the band is twisted through an 

 angle of about 45, so that when seen directly from behind the 

 ventral edge of the median arm forms a nearly straight line, while 

 the lateral arm is concave on its ventral surface and on its pos- 

 terior margin, Fig. 5, A and B. 



The position and structure of the mandibles clearly indicates 



p.s: 



FIG. 5. A, maxillae seen from ventral side and a little from behind. B, same 

 seen directly from posterior surface. X 4- 



that each mandible moved independently to and from the median 

 line, so as to bring their stout crushing and cutting edges into 

 apposition. They are frequently found with their posterior mar- 

 gins widely separated from the body, or even thrown forward in 

 front of the head with their ventral surfaces facing upwards. 

 Thus it is extremely probable that the mandibles, like two great 

 lids or covers, could swing forwards and backwards on the mem- 

 brane attached to their anterior margins, although it is improb- 

 able that they normally passed beyond the vertical position dur- 

 ing life, Fig. 2. 



The maxillae are usually widely separate in the median line, 

 and each was probably quite independent of the other. Their 

 form indicates that their movements were complex. They ap- 

 pear to have had a rotary movement on their long (transverse) 



