MIDLAND NATURALIST. 35 
The fourth and last preparation needed is easily made and it 
is done by the general method of cleaning diatoms—polycystina or 
sponge spicules. Take atest tubeand put into it some of the material, 
add some nitric acid and boil gently over flame. After the material 
is completely disintegrated add water to fill the test tube, and set 
aside for an hour and the spicules will settle to the bottom, where 
they willform asediment. Pour off carefully or with a long pipette, 
remove the water without disturbing the sediment. Wash t us 
several times to remove acid, alcohol may be used the third time as 
it hastens the next process. 
Take with a pipette a small quantity of the sediment and place 
a drop of it on the middle of a clean slide. Let it ary completely 
and pass the slide through a flame. Finally put on the balsam and 
cover and you have a permanent preparation of all kinds of 
spicules contained in the sponge. 
There remains for me only to note here all the species that have 
been so far observed in North America, I shall enumerate first all 
the genera so far observed in the whole world, secondly, I shall give 
the number of species belonging to each genus, and mention all 
the North American species in each genus. An abreviated and 
slightly modified key to the Genera of Fresh Water Sponges ac- 
cording to Potts-Carter System may be stated as follows : 
A Fresh Water Sponges with gemmules. 
I. Gem:mules with arotulate spicules. 
1. Gemmules surrounded by simple thorned spicules 
which are pointed or rounded at ends. . SPONGILLA. 
II. Gemmules with birotulate spicules. 
1. Birotulate spicules of one class or type and rotules 
equal OF DER S00 eee 
2. Birotulate spicules of two classes or types—the smaller 
number of them longer and rotules hooked. - 
HETEROMEYENIA. 
3. Birotulate spicules with rotules unequal. . TuBELLA. 
III. Gemmules with unirotulate spicules. 
I. Spicules forming capsule of gemmules with only one 
rotule other end merely pointed. . . . . PARMULA. 
IV. Birotulate spicules of no consequence. The foraminal 
tubules of the gemmules more or less prolonged and 
terminating in a funnellike expansion or divided 
into thread-like appendages varying in length and 
naea ee o” Cape 
