18 ITEW TOKK STATE MUSEUM 



seems of very doubtful propriety to attempt to carry out such dis- 

 tinctions in this genus, and it is proper to make this remark here lest 

 the outstanding ornamental variations not yet included under such sub- 

 divisions offer a temptation for the erection of parallel divisions. A 

 much more fundamental character is found to exist in many of these 

 Devonic Dalmanites, viz, the coalescence of adjacent members of 

 the first and second pair of glabellar lobes. This is a difference of 

 real significance in the anatomy of the animal, and it distinguishes a 

 considerable number of forms from the normal Dalmanites in 

 which the division of the lobes named is complete. 



In the species of the early Siluric such coalescence is obscurely 

 manifested, as in Dal. (Pterygometopus) eboraceus Clarke and 

 Dal. (Ptery.) intermedius Walcott, but here in association with 

 other characters which have been found a basis for a subgeneric distinction. 

 The upper Siluric was a period of full, typical development of Dal- 

 manites, and we observe that the Helderbergian species of the genus 

 maintain their typical character in this respect. Dalmanites stem. 

 mat us is the earliest Devonic form in which coalesence is pronounced. 

 Then follow Dal. anchiops Green and var. sobrinus H. and C., 

 Dal. regalis Hall, of the Schoharie grit, Dal. selenurus 

 Eaton, Dal. macrops Hall, Dal. diurus Green, Dal. calypso 

 Hall and Dal. myrmecophorus Green of the Onondaga lime- 

 stone. Within this group of species we find much diversity of mar- 

 ginal cephalic ornament : in Dal. macrops, Dal. calypso and 

 Dal. diurus the frontal border is undivided; in Dal. anchiops 

 it is moderately crenulated ; in Dal. selenurus it is divided into 

 incisor-like processes (Odontocephalus); in Dal. regal is the 

 processes are different and extend over the entire margin (Corycepha- 

 lus); in Dal. myrmecophorus the cephalic margin is not known, 

 but the pygidial margin is highly modified (Coronura). 



Turning to the Devonic species of this genus which possess the 

 typical separation of the first and second lobes, we may enumerate 

 Dal. pleuroptyx Conrad, Dal. dentatus Barrett, Dal. 

 d o 1 p h i Clarke, of the Helderbergian, Dal. boothi and var. 

 calliteles Green, of the Hamilton shales ; the first three bearing 



