388 MARINE INVERTEBRATES 



M. lapilloides. The shell in this species is about an inch in length 

 and has markings which give it a striking resemblance to granite. A 

 row of small round denticles upon the inner surface of the lip is a charac- 

 teristic already noticed in some of the west-coast murices. Their station 

 is the same as that of the purpuras between the tides on rocky, 

 exposed shores. (Plate LXXIII.) 



M. engonatum. This species has sharply ridged whorls, and re- 

 volving ribs with wavy growth-lines between them. In other respects 

 it is almost identical with the last described. It is often found mingled 

 with the seaweed which covers rocks between tides, and, when moist, 

 simulates the color of its surroundings. (Plate LXXIII.) 



GENUS Chorus 



C. belcheri. This family cannot well be left without at least a 

 mention of this large and rather handsome species. Chorus is a genus 

 of but few species, confined to the Pacific shores of North and South 

 America. This particular species does not reach as far north as San 

 Francisco, but may be taken at low tide in the vicinity of San Diego. 

 The prominent feature of the shell is the posterior canal, which, being 

 abandoned as the growth of the shell continues, leaves a series of hol- 

 low, folded spiny processes upon the shoulder of the body-whorl, which 

 appear like jagged points upon the spire. (Plate LXXIII.) 



FAMILY COLITMBEILIDJE 



This is a large family of small but often exceedingly beautiful 

 shells. Their distribution is mostly tropical, but the list of 

 North American species is a very generous one indeed if the 

 deeper-water forms are included. The animal is quite the same 

 as in the Bnccinidfe, to be described later. (See also description 

 of Bnccinum undatum on page 330.) The shells are usually quite 

 solid, with a long, narrow slit for an aperture ; the outer lip is 

 thickened on the inside, especially about the middle portion, and 

 is deeply toothed ; and the lower portion of the columellar lip 

 is also ribbed or toothed. 



GENUS Columbella 



C. mercatoria. This Antillean species is found in Florida, and is 

 one of the gems among the American shallow-water shells. Its height 

 is about one half of an inch. It is decorated with revolving grooves 

 and with a variously patterned color- scheme of broken yellow or reddish 



