DESCRIPTIONS OF NEW SPECIES. HI 



Surface marked by ordinary lines of growth, and also by somewhat 

 prominent folds parallel with them; the folds being stronger upon the 

 revolving prominences before mentioned than elsewhere, and disappear 

 upon the under surface of the shell. 



Greatest diameter of the largest example, twenty-eight millimeters ; 

 breadth of the same, twenty millimeters ; height, the aperture resting upon 

 the table, fifteen millimeters. 



By carefully digging out the stony filling I have been unable to find 

 any trace of a thickened inner lip such as characterizes the Neritidse, but 

 the body seems to be small, simple, and without even a proper columella. 

 The shell has the external aspect of a member of the family Neritidae, but 

 it is not without much hesitation that I refer it to the genus Neritina. 

 Indeed, this reference of it is made only provisionally until further investi- 

 gation can be made. This disposition of it is made partly because it seems 

 properly referable to no other established genus, and partly in view of the 

 facts published by Brinkhorst in his Monog. Gast. et Ceph. de la Craie Sup. 

 du Limbourg, 1861. In that work he describes and figures two species, 

 Nerita rugosa Hoeninghaus, and N. parvula Brink., which he shows to have 

 been so fossilized that the callus which formed the thickened inner lip was 

 entirely removed by a natural process of solution, leaving the remainder of 

 the shell intact, and in a condition similar to that of the species here 

 described as regards the absence of an inner lip, but natural casts of his 

 species showed that they originally possessed a well developed one. No 

 such casts have been found with our shells, and it is not improbable that 

 they were originally without any thickened inner lip. 



If so, our shell cannot be properly referred to any genus with which I 

 am acquainted, arid in case further investigation shall leave no doubt that 

 the shells have not been changed from their original character, I propose for 

 it the generic name of Lyosoma. 



Specific name given in honor of Prof. J. W. Powell, geologist in charge 

 of the Second Division United States Geological and Geographical Survey. 



Position and locality. Flaming Gorge Group; mouth of Thistle Creek, 

 Spanish Fork Canon, Utah. 



