THE MICROSCOPE. PALS 
more to the edge, as there is greater room there than in the other 
species, and, partly in consequence, it is not so transparent. Mr. 
Gosse says the eyes are small and transparent, but he figures 
them of a moderate size and red, and such Dr. Burn finds them 
to be. In the animal when closed, the edge is not everted, as 
in Mr. Gosse’s figure, but as in Fig. 2, the occipital margin is 
thrown into a fold, and the pectoral has a slit. When the head 
protrudes, the fold is pulled out, the slit opens to a v-shaped 
aperture, and the edge becomes everted. The lorica in this genus 
seems more flexed than in others ; as in pterodina valvata, the sides 
fold down like the ‘‘flaps of a pembroke table.” The foot protrudes 
through an opening like Fig. 3, almost at the extremity of the 
lorica, quite different from the other species, in which it comes out 
near the middle. 
BOTANY. * 
Tse Diarom Marsues anp Diatom Beps or THE YELLOWSTONE 
NationaL Parx.t—Mr. Walter H. Weed contributes an interesting 
article on this subject, the result of his observations while prosecut- 
ing geological work in the National Park. Here the writer found 
diatom beds of recent origin, covering many square miles, in the 
vicinity of the geyser and hot-spring basins. These deposits, which 
are among the largest fresh-water diatom beds of contemporary 
age known, are still forming by the growth of diatoms in the warm 
water marshes supplied by the hot-spring waters. Near the Emerald 
Springs at the Upper Geyser basin of the Firehole river, the most 
noted geyser region of the park, there is a typical marsh of this 
character. The waters have in times past encroached upon the 
neigboring patch of timber, killing the pines (Pinus murrayana), 
whose bare gray trunks stand upright in the ooze or lie scattered 
about half immersed beneath the waters of the marsh. A subse- 
quent half recession of the water has left a bare, white strip 
between bog and wood, on which vegetation has as yet a feeble hold, 
and the gaunt poles of the dead pines stand in a white powdery soil 
that is evidently a dried portion of the marsh mud. A large part 
of this bog is covered with a sparse growth of brackish water- 
plants, and the drier parts are grass-grown and form a fairly firm 
meadow bottom. The greater portion consists, however, of a semi- 
liquid, greenish-gray, dirty-looking ooze. Under the microscope this 
was found to consist of various diatoms, in which the Rey. Francis 
*Unader this heading will be included all Abstracts relating to the various depart- 
ments of Botany. 
+ Botanical Gazette, May, 1889, page 117. 
