eggs are attached. The latter are not all 

 in the same condition. Nearest to the 

 animal they are more or less fresh ; those 

 in the middle of the float contain embryos 

 and fully formed young, while those on 

 the outer end are empty, the young hav- 

 ing escaped into the water. The genus is 

 gregarious and may be found in almost 

 countless numbers. After a severe storm 

 they are sometimes cast upon the beaches 

 in vast numbers, where they soon die 

 under the fierce rays of the sun. 



We have thus far been dealing with 

 snails whose shells were formed in a 

 spiral coil. Quite a number of mollusks 

 are not protected by such a shell, its place 

 being taken by a fiat, shield-like disk, or 

 several distinct plates placed side by side. 

 The most familiar of the first is the Hmpet 

 or Patella, which is a depressed, conical, 

 oval disk, looking not unlike a miniature 

 shield. They live on rocks, to which they 

 cling with great tenacity. The animal 

 seems to have a pretty clear idea of local 

 geography, for it invariably returns to 

 the same place after its excursions for 

 food and the rock in some localities has 

 been hollowed out to a considerable depth 

 by the continuous dwelling thereon of 

 the limpet. The large foot is very strong 

 and it is almost impossible to dislodge 

 the shell from the rock when the animal 

 becomes alarmed and is aware that dan- 

 ger is near. While grazing along the 

 sides of a rock covered with fine sea- 

 weed, it will leave a track like a worm and 

 will clean ofif quite an area in a very short 

 space of time. 



Another species is the key-hole limpet 

 (Fissurella), distinguished by having a 

 slit or foram.en in the apex of the shell. 

 The shells of Fissurella are generally 

 rougher than those of Patella, and as a 

 rule they live in warmer seas. In the 

 limpet we find a departure from the gen- 

 eral form of both animal and shell, both 

 being bilaterally symmetrical, that is, 

 having both sides alike. In the mol- 

 lusks which have been presented thus far, 

 the body has been twisted in the form of 



a spiral, making one side different from 

 the other and causing the organs of one 

 side to become atrophied. In the limpets 

 the organs are paired, as they are sup- 

 posed to have been in the ancestors of the 

 living mollusks. 



The most peculiar of all the mollusks, 

 so peculiar, indeed, that they constitute 

 a separate order (Polyplacophora) are 

 the Chitons, or coat-of-mail shells. The 

 shell is made up of eight separate pieces 

 or plates, each locking with the other, the 

 whole supported by and buried in a coria- 

 ceous mantle which forms a margin all 

 the way around. This must not be con- 

 founded with the true mantle of the ani- 

 mal, for it is only a part of the shell. It is 

 beset with bristles, spines or hairs, which 

 add much to the peculiar appearance of 

 this mollusk. 



The Chitons live for the most part on 

 rocks at low water and are said to be 

 nocturnal in habit, feeding only at night. 

 Their movements are slow and they ap- 

 pear to be very sluggish in all their ac- 

 tions. When detached and taken from 

 their rocky homes they have the provok- 

 ing (to the collector) habit of rolling up 

 and are sometimes very difficult to 

 straighten out again. There are about 

 two hundred and fifty living species, 

 found in all parts of the world. 



In the foregoing pages we have called 

 attention to a few types of marine snails, 

 and what has been written has hardly 

 more than touched upon this vast field. 

 There are thousands of different species 

 even more interesting than those which 

 have been mentioned. There are the 

 beautiful ear shells, or Abalones, the little 

 periwinkle, so largely used as an article 

 of food in Europe, besides a host of 

 others too numerous to mention. The 

 brief notes and the figures on the plate 

 will convince the reader, it is hoped, that 

 these inhabitants of the deep are not only 

 beautiful and worthy of our attention and 

 study, but are also of much practical and 

 economical use to man. 



Frank Collins Baker. 



181 



