.
DISTRIBUTION IN TIME AND SPACE 235?
whole of the northern hemisphere ; one of the latter
occurred in SOuth AfriCa. It is generally agreed that the
—
remaining forms, Protopterus in the rivers of Africa and
Lepidosiren in those of South America, represent a higher. —
degree of specialization; They are in all probability,
…
therefore, of recent origin and their distribution »a“di‘dS
'
strong evidence in favour of the view that
South -
?
America were united until the Chalk period.
.
'
Reviewing now the occurrences _in the northern herni—
sphere during the ancient periode, we see that the rst
'
'
groups of the Diprioi and Ganoids were completely» Wiped
out before the end of the Palæozoic period. One group
of each, Ceratodontidæ of the former, Cœlzicanthidæ_0f the.
,
latter, lived in North America and Europe during the Meso—
'
zoic period, the latter right to the Upper Cretaceous. From
’
their shape and structure we may say that these were all
,
sedentary Îorms living in fresh water. Their nal extinction
occurred during the Chalk period,:when the
'
changes in the physical appearance of the ,world beganÏWhîch
‘
the upheaÿa1f0f
:_ranges
z
,
:
the
…
_'
Oflaiid…àtÏ
l
freshwaœr
populatænwasdestroyed:%ïî;'væf_
-j :
’
on“ theotherhandhoth ofthepelagi€mannetypes 'l- «fî:'î
escaped. Some of theClupeidsweretrapped
the Chalk as also somë'o'f the
_
interesting thing is,
”both tÿpejÿs
'
'
Ï began to break UP into OHShÛOÏS»'-WhiCh have bec0me. thé"
Ï__ _
the present day. But whereas
'
:
“Clupei—d type-ÏpeiäsiSted-5as' Well“ as its deseedante;in* thé
,
‘
deep sea or ffæhwa‘ter,‘ many of them losing the
f
_' _ï‘= ',or its'
With only one apparentexœp'
_
tion quite ',Changedi'their-mode
of
]
Îî'
__
op‘ed claspers, whilètthegRays Were only formed,probably
.
fr0in the
'during?théfChàlläfî—iäeÏrî,°d'
j
; The
j
m have
'
DISTRIBUTION IN TIME AND SPACE 235?
whole of the northern hemisphere ; one of the latter
occurred in SOuth AfriCa. It is generally agreed that the
—
remaining forms, Protopterus in the rivers of Africa and
Lepidosiren in those of South America, represent a higher. —
degree of specialization; They are in all probability,
…
therefore, of recent origin and their distribution »a“di‘dS
'
strong evidence in favour of the view that
South -
?
America were united until the Chalk period.
.
'
Reviewing now the occurrences _in the northern herni—
sphere during the ancient periode, we see that the rst
'
'
groups of the Diprioi and Ganoids were completely» Wiped
out before the end of the Palæozoic period. One group
of each, Ceratodontidæ of the former, Cœlzicanthidæ_0f the.
,
latter, lived in North America and Europe during the Meso—
'
zoic period, the latter right to the Upper Cretaceous. From
’
their shape and structure we may say that these were all
,
sedentary Îorms living in fresh water. Their nal extinction
occurred during the Chalk period,:when the
'
changes in the physical appearance of the ,world beganÏWhîch
‘
the upheaÿa1f0f
:_ranges
z
,
:
the
…
_'
Oflaiid…àtÏ
l
freshwaœr
populatænwasdestroyed:%ïî;'væf_
-j :
’
on“ theotherhandhoth ofthepelagi€mannetypes 'l- «fî:'î
escaped. Some of theClupeidsweretrapped
the Chalk as also somë'o'f the
_
interesting thing is,
”both tÿpejÿs
'
'
Ï began to break UP into OHShÛOÏS»'-WhiCh have bec0me. thé"
Ï__ _
the present day. But whereas
'
:
“Clupei—d type-ÏpeiäsiSted-5as' Well“ as its deseedante;in* thé
,
‘
deep sea or ffæhwa‘ter,‘ many of them losing the
f
_' _ï‘= ',or its'
With only one apparentexœp'
_
tion quite ',Changedi'their-mode
of
]
Îî'
__
op‘ed claspers, whilètthegRays Were only formed,probably
.
fr0in the
'during?théfChàlläfî—iäeÏrî,°d'
j
; The
j
m have
'