REVIEWS 287 
even provisionally as a fossil lamprey. Dr. Traquair’s objection that if 
Palaeospondylus be not a Marsipobranch it is impossible to refer it to 
any other existing group of vertebrates, Dr. Dean disposes of by boldly 
placing it in a new class by itself, elevating the order Cycliae, which 
Gill created for it, to that rank. Such a course may strike one as rather 
startling, perhaps, but it is certainly effective. An alternative propo- 
sition which Dr. Dean suggests may be more acceptable to some ich- 
thyologists “is to place it with Coccosteus as doubtfully its larval form.” 
Although there is considerable reason for regarding the variations in 
this small form as the early stages of some larger chordate, yet there 
is no direct proof that the adult form was an Arthrodire ; hence this 
association would have to be at best only provisional, and, in the author’s 
opinion, is inexpedient. As to the relations of newly exalted Cycliae 
to other classes, we are left as much in the dark as ever. Some very 
excellent figures of the fossil forms are given, together with a diagram- 
matic restoration. 
Very interesting, indeed, are the author’s views on the systematic 
arrangement of the early forms of fishlike vertebrates and fishes proper, 
with which the paper concludes. Amongst the latter the Chimaeroids 
are reduced again to the rank of an order instead of a subclass, princi- 
pally as the result of Dr. Dean’s recent embryological investigations, 
and the Dipnoi are reduced from class rank (Parker) to that of a sub- 
class. Acanthodes and Cladoselache are grouped together under the 
primitive Elasmobranch order Pleuropterygii. 
Turning now to the most primitive of all chordates, Dr. Dean ele- 
vates the Ostracoderms and Arthrodires each to the rank of an inde- 
pendent class, the former with its customary triple subdivision, but the 
latter separated into two new divisions, Arthrodira proper and Anar- 
throdira, which rank as subclasses. On the yround of their lacking a 
mandibular arch and paired limbs, the Ostracoderms were denied by 
Cope, and following him by Smith Woodward, and others, to be fishes 
at all, but organisms far removed from the latter, called ‘‘ Agnatha.” 
The origin and relations of the Ostracoderms are at present among the 
most important and fascinating questions of palaeichthyology. Dr. 
Traquair, in an extremely valuable memoir of last December" refuses 
to believe that these forms are Agnatha, declaring Cope’s view to rest 
entirely on negative evidence, and preferring to look upon the lowest 
«Report on Silurian Fishes (Trans. Roy. Soc., Edinburgh, Vol. YORNOIDS, IPE IO), 
1899. 
