38 THE NAUTILUS. 



ABNORMAL SHELLS 



BY L. E. DANIELS 



In the United States as elsewhere shells are frequently met with 

 that are abnormal to a greater or less degree due to the shell having 

 met with an injury during its growth. 



Tryon, in the American Journal of Conchology, Vol. 2, plate 1, 

 fig. 4, figures an abnormal specimen of Planorbis bicarinatus Say, 

 from the collection of Charles M. Wheatley Esq., of Phoenixville, 

 Pa., collected by him at Mexico, Oswego Co., N. Y. He says 

 " this is the first American specimen which we have observed to 

 deviate much from the normal form ; reversed or scalariform shells 

 being very much rarer in America than in Europe. Some of our 

 species of Lymnaa are sometimes slightly scalariform, and in the 

 Viviparida this is more frequent, but the deviation has never been 

 observed to be very great. Melantho Integra and decisa are both 

 occasionally met with, reversed. I believe that no scalariform Helix 

 has been observed in the United States, and the reversed specimens 

 known do not exceed ten or twelve." 



Thomas Bland in " Remarks on Certain Species of North American 

 Helicidae Part 3," 1862, says. "In one of my specimens of H. 

 tridentata, after completion of the shell, the animal continued the 

 last whorl about 2 mill beyond the lip, partially reflected the new 

 lip, and added two incipient teeth in advance of the old ones. On 

 plate 4, fig. 20 a sketch is given of the very singular reparation of 

 one of my specimens of H. septemvolva. The fracture was behind 

 the aperture, which the animal in consequence abandoned, but it 

 formed a new one by reflecting the outer lip, on the lower part of 

 which it added a small tooth, it found insufficient space for another 

 partial tooth behind the old aperture." 



Binney in the Manual of American Land Shells, page 282, fig. 

 300, figures an abnormal specimen of Stenotrema monodon. The 

 peristome having been broken after the animal's arrival at maturity f 

 a new peristome has been formed somewhat in the rear of the first, 

 and a new parietal tooth added. On page 291 he figures P. triden- 

 tata with a double peristome. 



S. C. Wheat in Bulletin of the Brooklyn Conchological Club 

 figures a specimen of Pyramidula alternata Say (fig. 5) found near 



