which constitute a prominent vertical ridge, on the summit of ag they 
interlock, forming a serrated suture. The other plates of the aree am- 
dulacrorum are much smaller, of more irregular shape a Ble 
but always, like all the other plates, e more or less hexagonal. All the 
plates of the aree ambulacrorum are ened by two holes, side by side, 
and all of them—not only those of the two larger central rows—very de- 
cidedly near the outer angle, or that angle farthest poe: the central ridge. 
These holes are placed irregularly; and generally I can only distinguish 
an inner vertical row of double pores, (those of the he tine ba 
and an outer one, next tothe are majores ; all the other pairs of pores are 
distributed more ‘irregularly over the surface, and it is with difficulty that 
I can make out something like four or five rows on each side of t 
middle ridge, which dwindle down to two or three rows towards the ends. 
vertical diameter, and very 
little less in the transverse. No trace of a stem has been found near per 4 
ippopotamus at Sierra Leone.— ompson, Esq., 
letter to J. E, Gray, Esq., mentions the existerice of a small (a 
tamus at Sierra Leone, w ich, as Mr. Gray states, is a fact of peculiar 
interest, since a new species from Liberia, of corresponding size, has 
been described by Dr. S. G. Morton. (See Proc. Acad. Nat. Sci. Phil., 
eb., 1844, and this Jouthalj xlvii, 406.) 
5. Tracks of Alligators; (Proc. Acad. Nat. Sci. Philad. )—Dr. 
clone oat aa fossil Pachyderms; (Proc. Acad. Nat. 
Sci. ‘Philad. se 1846. —Richard Ow en, Esq., haa. instituted the genus 
Harlanus for the species called Sus americanus by Harlan. _ It is de- 
scribed as approaching most nearly the tapiroid Pachyderms. The spe- 
ba is named by Mr. Owen, Harlanus americanus. 
IV. Astronomy. 
1. Observations on Shooting Stars, August 10, 1846.—During the 
nights of August 8-9th and 9-10th, 1846, tbe aay at this place was over- 
cast. The sky remained cloudy on the evening of the 10th, but never- 
theless, the observers (Messrs. L. W. Hart, J. H. Lane, W. Manl. Smith, 
an myself) sat up, in the hope of sere "favorable ehaakad during the 
night. Not long before midnight.the clouds passed off. Ta ing our 
— in the open air, we ee hed from OF a. m. to 2 a.m. of the Ith, 
and observed shooting stars — 
~ NEB. - eB 5. We BN. WwW. 
Aug. AM, Ob a, poet ar'e. 6128 an & pag 6 =14 
1 ausihied A. M. ‘Sica 9g 5 —32 
* An account of the St. Louis rocks, by Dr: Engelmann, will be found on p. 120, 
