Arthrodires 



591 



In a recent paper Dr. Otto Jaekel unites 

 Arthrodires and Ostracophores under the name 

 Placodermi. He regards Pteraspis as a larval 

 type, Asterolepis as one more specialized. In 

 Coccosteus he claims to find a pelvic girdle as 

 well as a more segmented skeleton. He regards 

 ah of these as true fishes, the Coccostcidcc as 

 ancestral, related on the one hand to the Cross- 

 opterygians, and on the other to the Stegocephali 

 and other ancestral Amphibians. 



Suborder Cyclise. — We may append to the Arthro- 

 dira as a possible suborder the group called CyclicB 

 by Dr. Gill, based on a single imperfectly known 

 species. Few organisms discovered in recent times 

 have excited as much interest as this minute fish- 

 like creature, called PalcFOspondylns guniii, dis- 

 covered in 1890 by Dr. R. H. Traquair in the 

 flagstones of Caithness in Scotland. Many speci- 

 mens have been obtained, none more than an inch 

 and a half long. Its structure and systematic 

 position have been discussed by Dr. R. H. Traquair, 

 by Woodward, Gill, Gegenbaur, and recently by 

 Dean, from whose valuable memoir on "The Devonian 

 Lamprey " we make several quotations. 



Palaeospondylus. — According to Dr. Traquair : " The 

 PalcBospondyliis giinni is a very small organism, usually 

 under one inch in length, though exceptionally 

 large specimens occasionally measure one inch 

 and a half. ... It has a head and vertebral 

 column, but no trace of jaws or limbs 

 and, strange to say, all the specimens 

 are seen only from the ventral aspect 

 as is shown by the relation of the 

 neural arches to the vertebral 

 centra. 



" The head is in most cases 

 much eroded. ... It is di- 

 vided by a notch . . . into 

 two parts. . . . The anterior 



Fig. 369. — Palnospondylus gunni Tra- 

 quair. Devonian. (After Traquair and 

 Dean. ) 



