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antennaD. The first pair of legs is small. The second is the strongest, and 
bears small chelae, and projects five mm. beyond the margin of the thorax. 
The third and fourth pairs are weak ,* the fifth of double the strength and 
size of the previous one. The abdominal segments agree exactly in outline 
with those of Palaemon; as also do the five-leafed tail-fin. 
The Immense Coal-area of the United States. — Professor Hitchcock gives 
in the ‘‘ Geological Magazine ” (March) a good sketch of the vast coal 
deposits of America. He states that the total area amounts to 230,659 
square miles ; no notice being taken of any coals which do not belong to 
the Carboniferous system. There, are many others of commercial impor- 
tance, as the Triassic of Virginia, the Cretaceous of the Territories west of 
the Missouri Piver, an immense amount in California, Alaska, &c. These 
facts will afford data for those who are interested in estimating the amount 
of coal in different countries by the number of cubic miles or tons. The 
statements are too brief to permit any notice of the best or of the inferior 
coal. — [Over from the last Number of P. S. P.] 
Limnloid Crustacean Footprints. — Dr. J. W. Dawson, writing on this 
subject in an American Journal, says, that as these crustaceans are well 
known in the carboniferous beds of Europe and America, their footprints 
might be expected to occur in rocks of this age, but the first he has met 
with were sent to him last summer by his friend Mr. Elder, of Harvard 
College, who found them quite abundantly in dark-colom’ed fiag-stones be- 
longing to the Millstone Grit formation at McKay’s Head, in Nova Scotia. 
The animal which produced these marks must have been of small size 
(about half an inch in breadth), in this agreeing with the usual size of the 
Coal-formation Limuloids ; and like the ancient Protichnite-makers, it left 
. no trace of the edges of the carapace, but a very distinct impression of a 
sharp-pointed tail. Its posterior feet had three or possibly four sharp toes. 
There were besides several pairs of sharp-pointed walking feet. On the same 
slabs there are some series of marks, evidently made by the same kind of 
animal, which have no tail-mark, and there are tail-marks with only traces 
of those of the toes. It is worthy of notice that, though these tracks indi- 
cate the presence of the animals, no crusts of Carboniferous Limuloid 
crustaceans have yet been found in Nova Scotia. The sand in which the 
tracks now referred to were made was probably too hard to permit the 
swimming feet to make any impression. With respect to the absence of the 
marks of the sides of the carapace, he considers that the genus Belinurus of 
the Carboniferous had the sides of the carapace less deep than that of the 
modern Limulus, and this may also have been the case with the more 
ancient Limuloids of the Potsdam. See as to this subject a letter by Prof. 
Hall in the Canadian Naturalist,” 1862. 
The Rate of Growth of Coral Reefs has been recently attempted to be 
ascertained by the researches of M. N. Le Clerc and De Benaze, who have 
published a small work on the subject in French [Publisher, Laine, rue des 
Saints-Peres 19, Paris]. They attempted to ascertain the rate of growth 
of the coral reef at Tahiti, called the Dolphin Shoal, by measurements from 
the level of the stone planted on the shore on Point Venus by Capt. Wilkes, 
and comparing their results with his. They made measurements : but they 
observe that Wilkes does not state whether he measured from the top of a 
