59 
the most part in shallow quiet bays and usually on a rather sandy 
bottom. Its ordinary height is from two to eight inches. A 
close relative of Penzcillus is Rhipocephalus. When living, the 
plants of this genus look somewhat like little spruce or fir trees 
growing on the bottom of the ocean. In tropical regions, espe- 
cially in association with coral reefs, many of the marine plants 
are more or less coated or permeated with lime. This calcareous 
coating is exhibited among the green algae not only by Penicillus 
and Rkipocephalus, but also by the fan-shaped Udoteas the opun- 
tioid or vertebrate Halimedas, the worm-like Meomeris, and the 
. Fic. 10. The Mermaids’ Wine-glass, Acetabulum crenulatum (Lamout. ) Kuntze. 
From Bermuda. ( 1 size. ) 
dainty Acetabulum. All of these lose their natural green color 
very soon after being exposed to the light and are left a chalky 
white. The most strikingly beautiful of these calcified green 
algae are doubtless the species of Acetabulum. The plants of 
this genus look like dainty mushrooms or like tiny everted 
umbrellas, In the American species illustrated by the accompany- 
