144 O. R. Eastman — Asterolepid Appendages. 



its complement of ossified ribs, has a purely mythical existence. 

 There are no vertebral rings, the axis being entirely cartilagi- 

 nous, and on either side of this occur the neural and haemal 

 arches. It is the latter which Jsekel has represented as ribs. 

 Neither is there a pelvic girdle, as claimed by this author, his 

 so-called " ileum " being erroneously interpreted as such, and 

 inverted in position. The narrow, rod-like portion, instead of 

 being directed dorsally, and attached to the cartilaginous axis, 

 in reality projected outward from the body-wall, being in fact 

 merely a modified anterior fin-ray. There is a well-preserved 

 specimen in the Paris Museum of Natural History which shows 

 these structures in their natural position, followed by the 

 remaining fin-rays in regular sequence; nor is this the only 

 example which confirms the interpretation here given. 



Another notable difference between Arthrodires and Astero- 

 lepids consists in the structure of the dermal plates covering 

 the head and anterior part of the trunk. The body-armour of 

 Asterolepids very likely originated from the fusion of scales, 

 but Arthrodires are naked without exception, and it can be 

 demonstrated that their dermal plates arose within the integu- 

 ment from secretions on both sides of the initial layer. The 

 process was continuous throughout life, a succession of tuber- 

 culated strata being deposited upon the external surface of the 

 earlier formed laminae, and bony tissue being added underneath, 

 also in regular layers. Altogether, the distinction between 

 Arthrodires and Ostracophores is so trenchant and far-reach- 

 ing, that the revival of the group "Placodermata" for their 

 union appears to be an unwarranted and decidedly retrograde 

 movement. Finally, we must beg to differ from Mr. Regan in 

 his conclusion that "the Coccosteidw are Teleostomi, that the 

 Asterolepidw are allied to the Coccosteidw, and that the Cepha- 

 laspidce have been derived — through the Tremataspidce — from 

 the Asterolepidw" this view being unsubstantiated by either 

 morphological or palseontological evidence, and contrary to all 

 probability. Nor can we view with much favor Jsekel's 

 extraordinary hypothesis* that Coccosteans are ancestral to 

 Chimgeroids. 



Harvard University, Cambridge, Mass. 



* Jsekel, 0., Ueber Kamphodus, etc. (Sitzungsber. Gesell. Naturforsch. 

 Freunde, p. 392), 1903. 



