May 27, 1915] 
NATURE 
3355 

on the same horizon. The Alaskan beds (p. 43) are 
“probably not older than the Bathonian and certainly 
not younger than the Oxfordian.” 
E. Wilbur Berry (ibid., 84, 1914) issues a report on 
the Upper Cretaceous and Eocene floras of South 
Carolina and Georgia. Ficus is represented in the 
Cretaceous beds of South Carolina by five species, and 
the willow, the oak, the myrtle, and the laurel are 
among the numerous angiosperms present. The 
author (p. 71) regards this flora, the post-Raritan 
floras of the eastern States, and the major part, at 
least, of the Dakota flora, as Turonian and not Ceno- 
manian in age. The Cretaceous flora of Georgia 
. 127) is placed on the same horizon. <A small 
Middle Eocene (Claiborne) flora of seventeen species 
allows of an interesting discussion of Cainozoic climate 
in the eastern States. The main features of the 
modern flora of tropical America extended as far 
north as latitude 33° in Middle Eocene times, and 
retreated later towards the West Indies. In the same 
paragraph on p. 161, this retreat seems to be dated 
as ‘‘toward the close of the Tertiary,’ and also, on 
Dall’s evidence from marine life, as ‘‘at the close of 
the Oligocene.’ The bibliography is useful to all 
workers in early Cainozoic floras, including that of 
Bovey Tracey in Devonshire. 
David White (ibid., 85-E, 1914) emphasises the 
occurrence of thread-like resinous casts in ‘‘ mother 
of coal” and other Paleozoic ‘“‘coals of high rank,” 
associated in places with megascopic lumps of resin. 
By the decay of the plant tissues (p. 82), these resinous 
infillings of secretory canals have become concen- 
trated in undue proportion in the coals. 
A paper by F. W. Clarke and W. C. Wheeler 
(ibid., 90-D, 1914) has a bearing on the occurrence 
of magnesium carbonate in rocks. It discusses ‘‘ The 
Composition of Crinoid Skeletons,’’ and twenty-one 
species, representing as many genera, are shown to 
utilise in their hard parts from 7-28 to 12-69 per cent. 
of magnesium carbonate, when organic matter is 
eliminated from the analyses. A specimen of Hathro- 
metra dentata includes, moreover, 5:73 per cent. of 
silica, a substance usually present in quantities of 
about o-1 per cent. When arranged by localities, it 
is seen “that the proportion of magnesium carbonate 
in crinoids is in Some way dependent on temperature ”’ 
(p. 36). Shallow water in the tropics gives the 
highest percentage. The calcium carbonate is always 
in the calcite state. The investigation of fossil 
crinoids, from the Lower Ordovician to the Eocene, 
shows nothing higher than 2:56 per cent. of mag- 
nesium carbonate, except in a Triassic form, Encrinus 
liliiformis, which yields 20-23 per cent. We may con- 
clude that the matrix was in this case dolomitic. 
It is suggested that infiltration of calcium carbonate 
has reduced the proportion of magnesium carbonate 
present in fossil specimens. The organic matter in 
recent forms, often amounting to 15 per cent., would 
certainly allow of the substitution of some other mate- 
rial during fossilisation. 
Ivor Thomas’s first section of his revision of ‘‘ The 
British Carboniferous Producti’ (Mem. Geol. Survey 
of Great Britain, Palzontology, vol. i., part 4, 1914) 
covers the genera Pustula and Overtonia, which are 
here established (p. 259) on Productus pustulosus and 
fimbriatus respectively. But the special importance of 
the memoir lies in the review of the Producti gener- 
ally, based on the work of several years. Doubt is 
thrown (p. 229) on the clasping nature of the spines 
of Productus, and it is suggested that a spine during 
growth may occasionally be diverted by an adjacent 
object, so as to appear to fold around it. Both ex- 
ternal and internal features of the shells are discussed 
in relation to the animal as it lived, and no apology 
NO. 2378, VOL. 95| 


is needed for the consideration of the general prin- 
ciples of mutation and the meaning of species, ques- 
tions that have naturally forced themselves before the 
philosophic author. 
It is interesting to note, in L. W. Stephenson’s- 
study of the ‘‘Species of Exogyra from the Eastern 
Gulf Region and the Carolines” (U.S. Geol. Survey, 
Prof. Paper 81, 1914) that the genus was first described 
by T. Say in 1820, the type being Exogyra costata 
from the Cretaceous of New Jersey. The ‘‘Sby.” 
after the name in Woodward’s ‘Manual of the 
Mollusca,” 1851, is probably, a mere misprint. E. 
costata is shown regularly to succeed FE. ponderosa, 
the species having thus a zonal value. The strata are- 
described in the same memoir. 
In vol. xlii. of the Records of the Geological Survey 
of India (1912, p. 1), R. Bullen Newton and E. A. 
Smith have directed attention to the survival of a 
well-known Miocene oyster, Ostrea gryphoides 
(=crassissima), in recent marine deposits under Cal- 
cutta and in the Bay of Bengal. 
Passing to arthropods, C. D. Walcott gives us a 
new genus of trilobites, Saukia, with numerous 
species, separated from Dilkellocephalus by the posses- 
sion of a longer glabella and pygidium (‘ Dilkelo- 
cephalus and other Genera of the Dikelocephalinz,”’ 
Smithsonian Miscell. Coll:, vol. Ivii., 1914, p. 345). 
On p. 363 the author explains the common retention 
of D. D. Owen’s spelling of Dikellocephalus with a 
single “1,” under a rule that was surely established 
by persons with limited glabellas. Osceolia and. 
Calvinella are here founded on D. osceola and D. 
Spiniger (p. 388) respectively, though on p. 365, prob- 
ably by a slip, the latter species is referred to Saukia. 
It seems from p. 364 that Walcott is unwilling to 
recognise Dikellocephalus from any locality outside 
the United States, and this should lead to a new 
examination of British and other European forms. 
The Devonian faunas of South Africa and South 
America receive a new link in the discovery by S. J. 
Shand of a species of the Brazilian trilobite Pennaia 
in the Boklkeveld Beds of the Hex River in the- 
Cape Province (Trans. Geol. Soc., S. Africa, vol. 
XVil., I9I4, p. 26). 
Alexander Petrunkevitch has produced ‘‘A Mono- 
graph of the Terrestrial Palaeozoic Arachnida of North 
America’ (Trans. Connecticut Acad. Arts and 
Sciences, Yale University Press, 1913). This is a 
systematic review, not quite so extensive as its title 
would imply, of the American Palzeozoic types of 
scorpions and spiders, involving the establishment of 
new genera and species. The author directs attention 
(p. 20) to the recent work of Clarke and Ruedemann, 
which indicates a relationship of the eurypterids with 
the succeeding limuloids, rather than with the 
scorpions, although the three groups may have had 
separate ancestors. The Carboniferous  arachnid 
faunas of Europe and North America are stated to- 
be distinct (p. 26); but both have a more tropical 
character than is found locally in their modern repre- 
sentatives. The “excellent photographic plates ajre 
from specimens developed with much care by the 
delicate chiselling away of flakes of rock in order to: 
reveal appendages. 
R. Broom records (Bull. Amer. Mus. Nat. Hist., 
vol. xxxii., 1913, p. 563) his studies of a number of 
Permian labyrinthodont skulls in the American 
Museum, in which he has succeeded in tracing sutures 
hitherto obscure, and thus in providing new descrip- 
tions of the cranial elements. 
R. S. Lull describes (Amer. Journ. Sci., vol. xxxvii., 
1914, p. 209) a ‘Fossil Dolphin from California,’ 
which is presumed to be of Miocene age. The speci- 
men is placed under the living genus Delphinus, 
