SHELLS WITHOUT CANALS 221 



is delicate as a skein of silk. The marine plants are 

 very interesting, every one of them, and are worthy 

 of careful study. As we ramble among the rocks 

 seeking after shells it is pleasant to know and admire 

 the plants among which they are most likely to be 

 found. 



Acm(za instahilis^ Gld., the Unstable Seaweed- 

 Limpet, is larger than the last species. The shell is 

 more limpet-shaped, but it is narrow and compressed 

 at the sides; its surface is smooth, and its color is 

 brown on the outside and white within. Its length is 

 three-fourths of an inch. 



AcmcEu depicta^ Gld., the Painted Limpet, has a 

 very narrow shell, with straight, flat sides. In color 

 it is nearly white, with fine brown stripes radiating 

 from the apex. It is a little shell, being only from 6 

 to 12 mm. in length. It is a southern species, and it 

 may be found at low tide clinging to the tough and 

 narrow blades of grass which grows in certain 

 shallow places along the edge of the sea. This so- 

 called eelgrass is not a true grass at all, but a species 

 of Zostera, which belongs to the Pondweed family. 

 But it does produce true flowers and seeds, though 

 they are not very conspicuous, and that is more than 

 most of the plants which grow in salt water ever do. 

 All the seaweeds are mere algae, and they reproduce 

 by means of spores, which are far simpler objects 

 than seeds. Moreover they lack certain organs, not- 

 ably a vascular system, or set of little tubes, which 

 the higher plants always possess. Cut one of the sea- 

 weed stalks across and you will see that it is very 



