No. 444.] P TERA SPID/E AND CEPHALASPIDAZ. 859 



by a small pit on the under side of the dorsal shield, in Tolypele- 

 pis by an inconspicuous smooth spot on the outer surface, and 

 in Cyathaspis by three obscure markings. These conditions 

 indicate a considerable degeneration of the visual organs in these 

 genera and must have profoundly modified their mode of life 

 toward one of less activity and greater simplicity. We have 

 here a condition approaching that of the lampreys, where the 

 lateral eyes may be nearly functionless, while the median ones 

 attain a degree of development that is hardly exceeded by that 

 in any other vertebrate. 



In Cephalaspis, the mouth was almost certainly situated high 

 up on the vaulted under surface of the head and the character 

 of the mandibles, as well as the small space into which such 

 organs must have been crowded indicates that the mouth was 

 very small. Similar conditions prevailed in Tremataspis, Bothri- 

 olepis and other members of the ostracoderms. Under these 

 conditions and with their necessarily slow and clumsy move- 

 ments, the ostracoderms could not have been rapacious animals. 

 The position of their eyes, whether well developed or not, points 

 with equal decisiveness to the same conclusion, for whether 

 swimming or crawling, they could not see where, or when, to 

 seize their prey, because their eves would always be behind their 

 own body. They must have been dependent on highly spe- 

 cialized gustatory, or tactile, organs situated near the mouth. 



As a parasitic life for such animals is out of the question, it is 

 probable that they lived on the soft bodied animals or decom- 

 posing organic matter that could be exposed or forced into the 

 mouth as they slowly ploughed their way through the soft mud 



Dartmouth College, Hanover, N. H. 

 July 10, 1903. 



