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TOPULAR SCIENCE REVIEW. 
number of mollusca — 1 Pteropod, 15 Gasteropoda) 188 Bivalves, and 5 
Brachiopods — and species of Nautilus and Baculites also occur. Of other inver- 
tebrate groups Dr. Philippi notices Annelids, Echinoderms, and Zoophytes, 
or rather Bryozoa ; whilst the vertebrata are represented by a few fish- 
remains, a Plesiosaurus and a whale. Of the eighty-one genera of mollusca, 
three, namely Baculites , Cinulia, and Tngonia , may be regarded as showing 
Cretaceous affinities, and the Baculites and Plesiosaurus chilensis , especially, 
have been regarded as more properly belonging to the Cretaceous series. 
Dr. Philippi has, however, obtained specimens of both species along with 
undoubted Tertiary fossils, and hence he is inclined to draw a parallel between 
the phenomena presented by this part of the geological series in Chili and 
in New Zealand, where, as is well known, Dr. Hector recognizes what he 
calls “ Oretaceo-tertiary ” strata. From the scarcity of forms proper to warm 
climates, and especially the absence of corals and Polythalamia, Dr. Philippi 
infers that at the period represented by these beds there may have been 
already a cold current flowing to this region from the Pole. An interesting 
point which comes out from his table of the molluscan genera is that the 
tertiary fauna of Chili possessed a much greater similarity to the existing 
fauna of the Mediterranean than to that of the neighbouring coasts. It 
included at least twenty-five important genera, now entirely wanting on the 
Chilian coast, but all, with the exception of Perna , represented in the Medi- 
terranean. 
Among the remains of fish, which are generally so fragmentary as to be 
incapable of determinination, Dr. Philippi records the discovery of the tooth 
of a species of Carcharodon , which is interesting from its relationship to the 
gigantic teeth belonging to the same genus found in the Tertiaries of the 
Mediterranean region. The author describes it as belonging to a distinct 
species under the name of Carcharodon gigas ; it differs from the well-known 
Carcharodon megalodon at first sight by its obliquity; its convex side is 
obtusely ridged, and its margins are less regularly and less deeply notched 
than those of the European species. The length of the longer margin of the 
tooth was about 4£ inches. 
Polydactyle Horses. — Professor Marsh has an article on this subject in the 
11 American Journal ” for June 1879, which, besides describing his observa- 
tions on recent horses with supplementary digits, gives an interesting sum- 
mary of the palaeontological facts bearing on the question of the supposed 
parentage of existing Solidungulates. It appears that the most common 
form of polydactylism in living horses is the presence of an extra small toe 
and hoof on the inside, either of the anterior pair or of all four feet, but 
Professor Marsh has lately heard of a colt with three toes on one fore foot 
and two on the other, and of a mare (still living) which has three toes on 
each fore foot and a small extra digit on each hind foot. The more frequent 
presence of extra digits on the fore foot is what might be expected ; but the 
abnormal development of the toe on the inside is curious, both because in 
general the second digit is less persistent than the fourth, and because, when 
developed, it would seem to be rather in the way. 
Of the American series of precursors of the horse, Professor Marsh speaks 
as follows : “ If we examine the remains of the oldest representatives of the 
horse in this country, we shall find that these animals were all polydactyle 
