NATURAL HISTORY MISCELLANY. 159 
Their hard silicious shells are characterized by being marked with 
fine delicate lines or rows of dots. They are found in all our waters, 
whether salt, brackish, or fresh. Their hard shells are preserved un- 
er bogs, where they form layers, resembling fine white silicious sand, 
and also in guano. They also occur fossil at Bermuda, Oran in Alge- 
ria, and Richmond, Va. i 
` OBJECT TEACHING IN NATURAL Scrence.—I am strongly of opinion 
that it is more necessary than ever that we should teach as much as 
possible by the eye. In teaching any branch of natural science, the 
; demonstration should be combined with oral teaching. T nt 
4 hould at is ribed, and where it is not possible for th 
teacher to exhibit illustrative specimens, good a drawings, and 
explanatory diagrams should be supplied. It is e 
teacher to study how to communicate knowledge most easily and most 
clearly, E8 to save the student as much time as possible ; for it is not 
likely that the amount of work which is required by the various ex- 
Dg boards will be reduced, nor indeed is it desirable that it 
should be. Iti is, therefore, incumbent upon teachers to facilitate the 
Such a system adds greatly to the interest of lectures, and ena 
the student to acquire a correct idea of structure, which it is ‘aie 
2 sible for him to obtain by reading, or from mere description with the 
e. aid of diagrams. — Bra EALE’S ‘‘How to Work with the Microscope.” 
—o 
SCIENTIFIC EXPEDITIONS. 
Mr. C. F. Hartt, now lecturing on Natural History in New York 
City, who gained much experience as an explorer in Brazil, in the late 
Thayer Expedition to the Amazon, under the conduct of Prof. Agassiz, 
purposes in a few weeks to visit anew the coast of Brazil, and study 
_ the coral reefs perry crete discovered by him, and also the marine fauna 
of these shores. Mr. Hartt goes thoroughly prepared for these im- 
portant 
a ey; and also as a student and assistant for several years in the 
Museum of Comparative Zoölogy, at Cambridge. 
k Mr. J. F. Allan, of Springfield, Mass., author of a series of ornitho- 
_Papers now publishing in the NATURALIST, and also one of 
