PALEONTOLOG'IC CONTRIBUTIONS 



147 



eyes. The broad, netlike brim served to support the animal on the 

 soft mud, preventing its complete burial in the latter, and the bulg- 

 ing glabellar lobe was necessary to provide room for the capacious 

 stomach in an animal that gorged itself with the mud to extract the 

 organic matter (see Jaekel, no. 5). As the broad brim extended 

 horizontally all around the head, the rostrum had to be forced 

 backward and up the frontal part of the glabella and the stress 

 upon the frontal lobe from the growing stomach assisted in draw- 

 ing the rostral piece into its present position. 



Fig. 46 Cryptolithus tesselatus 



Green. Diagrammatic restoration of head shield. 

 a, frontal facial suture; b, lateral facial suture; 

 c , lateral eye tubercle ; d, median eye tubercle ; 

 e, frontal tubercle; f, frontal pores in dorsal 

 furrow (olfactory organs?) 



If this view is correct, we see in the suture line upon the frontal 

 lobe another piece of the facial suture, whose connection with the 

 posterior section of the free cheeks is broken, however. This, we 

 believe, is also due to the gradual expansion of the brim backward, 

 which also forced the anterior of the two suture lines, now leading 

 to the rudimentary lateral eyes more and more backwards, extend- 

 ing the anterior portion of the fixed cheeks continually backward at 

 the expense of the free cheeks. In other words, it appears probable 

 that the free cheeks were originally much broader and extended 

 much farther forward with their anterior margin, passing in front 

 of the glabella, where they cut off a rostral piece. The narrow 

 vestigial free cheek carrying the rudimentary lateral eye is then 

 only a secondary phenomenon due to the excessive broadening of 

 the head. We see in this further evidence of the extreme adapta- 

 tion of the Trinucleidae from formerly normal Opisthoparia. 



