i 1887] Geology and Paleontology. 1015 
_ Pterichthys, and Bothriolepis in this “sub-class” is certainly a 
= violation of the precision of definition which all true systems 
should possess. Dr. Zittel says indeed of the Pteraspidide that 
their position is entirely undecided. The “orders” of “Ga- 
noidei” we find to be unnatural in various respects. We also — 
object to the use of family terminations for orders, and ordinal 
terminations for families, which the authors of the work have 
ed 
opted. 
The fulness of this part of the subject as presented by Professor 
Zittel enables the reviewer to give a synopsis of his own views 
on the subject of the classification of the lowest Vertebrata, to 
which he has hitherto only contributed fragments.’ This is now 
done in anticipation of a fuller memoir with complete illustrations. 
Preliminarily, the following point, originally propounded in 
substance, I believe, by Professor Haeckel, is adhered to: 
eo cee vertebrate which lacks the mandibular and scapular arches 
ta 
= _ On this account I have declined to include in the Pisces such 
_ forms as the Pterichthyide and Bothriolepidide, also the Pteras- 
_ Pidide and Cephalaspididze, but have referred the latter of them 
_ tothe Haeckelian class Agnatha, which also includes the Mar- 
= Sipobranchi, or lampreys. (See NATURALIST, 1886, 1027. 
© AL The primary divisions of fishes are indicated mainly by thew 
cranial structure. 
This is an expression of the fact generally admitted by zoolo- 
gists, that there are at least four primary divisions so de ned,— 
_ Wiz, the Holocephali, the Dipnoi, the Selachii, and a fourth di- 
_ “sion, which was first named by Professor Sir Richard Owen, 
the Teleostomi. 
M. The divisions of the Teleostomi are indicated by fundamental 
difications of their fin-structure. 
A This taxonomic truth was first insisted on by the writer (Zi =: 
er. Philos. Soc., 1870, p. 445), and is now repeated with em- 
>: He probably correct evolutionary patito of Dohrn re- 
k € fins as remains of three or four primitive a 
 “Piblastic folds, which have been biori by mesoblastic 
y i F 
 Sificati “atsactions of the American Philosophical Society, 1870, p- 4453 ° 3 
pacal no , Adv. 
w, reat the Extinct Fishes of the Lower Types,” Proceni: AD iay p 
37, > P 292; “On an Interesting Genus of Chordata, aturalist, E 
