TROCHISCUS. 87 



berosum, Chem., Pack-i-po'-ma gib-ber-o'-sum, a 

 mollusk that is seldom found alive. The shell is 

 broadly conical; its whorls are quite rough, and its 

 flat base is marked with five or six deep, concentric 

 furrows. As the shells are usually dead and some- 

 what broken, it is seldom that you find the operculum 

 in place. This operculum is quite different from any 

 which we have noticed before, and is of an oval shape, 

 and is made up of a plate of horn for the inside, and 

 a solid bulge of shell for the outer part. They may 

 frequently be picked up along the beach, and are 

 puzzling objects to those who have never seen them 

 in place. The shell is usually from two to three 

 inches in breadth across the base, and of about the 

 same height. 



A much smaller shell, but similar in some respects, 

 is that of Leptonyx sanguineus, Linn., Lep'-to-nyx 

 san-guin'-e-us, shown in Fig. 73. The largest speci- 

 mens are of the size of a pea, but many 

 smaller ones will be found. The whorls are 

 few, marked with fine, distinct, spiral ridges ; 

 Fig. 73. operculum solid and shelly. The color is 

 reddish, sometimes faded or banded. 



This species may be found at low tide, living upon 

 rocks; but the Hermit Crabs bring up many empty 

 shells. You notice that the name of this species was 

 given by the great Linnaeus. Probably he never saw 

 a specimen from the Pacific ; but ours is considered 

 identical with the Mediterranean species to which he 

 gave the above name. 



Leptonyx baaila, Cpr. , back'-u-la, is another spe- 

 cies. In shape it is like the last shell, but it is 

 smaller, being only about one-eighth of an inch in 

 diameter. It is nearly smooth, dark or ashy ; 

 southern. 



