324 Shell Life 



Nautilus Trumpet-snail (P. nautileus) is much 

 smaller that P. glaber, its shell measuring only one- 

 tenth of an inch across. It is a dull brown, slightly 

 concave above, slightly convex beneath, bluntly keeled, 

 and the whorls ridged across, the ridges projecting 

 on the keel " like the rowels of a spur," as Jeffreys 

 has it. The mouth is an oblique oval, and the 

 umbilicus is very large. In spite of its minuteness, 

 its sculpturing makes it a handsome shell. The 

 animal is very inactive ; it feeds on decaying water- 

 plants in marshes, ponds, and ditches. A good plan 

 in collecting it is to carefully pull up some rooted 

 aquatic plant and wash its base and roots in a jar of 

 clear water, when — if P. nawtileiis is present in the 

 pond — a large number of specimens will be found at 

 the bottom. 



A species closely allied to P. nautileus was in- 

 troduced from America, it is believed in cotton-bales, 

 in the year 1869. In that year Mr. Thomas Rogers 

 of Manchester noticed it in the refuse water from a 

 cotton-mill. It was identified as P. dilatatus, an 

 American species about the same size as P. nautileus, 

 but with one whorl less, the under-side swollen, the 

 mouth large and squarish, the outer lip dilated, and 

 the umbilicus small but deep. Since the year of its 

 discovery it has largely increased both in numbers 

 and the area occupied in the Bolton Canal at 

 Pendleton and Gorton. Its naturalisation illustrates 

 how easily even minute and delicate aquatic animals 

 may get carried across thousands of miles of salt 

 water to new homes. 



The remaining species of this interesting genus is 

 the Shining Trumpet snail (P. coinplanatus), formerly 



