THE SHELL-FISH OF THE COAST. 31 



very common (cylindrical) small shell that is found 

 almost everywhere among the tide-water sedges or 

 grasses. The latter is the Melampus bideniaius (PI. 

 1, fig. 2), an air-breathing or pulraoniferous mollusk, 

 like the common garden-snail, but requiring a cer- 

 tain amount of salt water for its happiness. "Why 

 this should be necessary is not exactly known, the 

 animal breathing by means of a true lung, as in 

 the case of all true land-snails (Pulmonata). The 

 slipper-limpets are readily recognized by their some- 

 what boat-shaped shells, which are found either 

 loose by themselves, or attached to other shells and 

 stones, their outlines being largely modified accord- 

 ing to the receiving substance. This modification 

 extends in such varying directions that it is not yet 

 clear what proportion of the ordinarily accepted spe- 

 cific characters is founded upon it. For the pres- 

 ent, however, we recognize some three or four spe- 

 cies as occurring on our coast : Orepiduh, fomicata 

 (PI. 1, Fig. 15), the largest forrp, which not rarely 

 measures an inch and a half, or more, in length; 

 Crepidula glauca or eonvexa (Fig. 25), a small humpy 

 shell, whose presence appears to be generally asso- 

 ciated with that of the small hermit and of Nassa 

 obsoleta; and Orepidula plana or unguiformis {Fig. 26), 

 with a nearly flat shell, which is frequently found 

 within the apertures of other shells. The slipper- 

 limpets have the habit of crowding upon themselves, 

 or of 'bunching,' so to speak; they may accord- 

 ingly be picked up in accumulated masses, and this 

 is especially true of the more northerly shores. 

 Closely related to the preceding is the crucible- 



