LYMISLEHXE OF NORTH AMERICA. 103 



HORIZON : Cache Valley beds, Humboldt Group, Pliocene Period, 



LOCALITY: Cache Valley, Cache County, Utah. 



REMARKS: 'This species is remarkable for having its surface 

 ornamented by a very regular, vertical costse, quite strongly defined 

 on its body-volution. This character will readily distinguish it from 

 any other species, either recent or fossil, known to me, and, with its 

 other characters, forbid its reference to any of the established sub- 

 genera. In the possession of ribs, it agrees with Pleurolimncea, but it 

 differs extremely in form from that type. I have therefore proposed 

 for its reception a new subgenus under the name Polyrhytis. 



"I have seen but a single specimen of this shell, consisting of a 

 well-defined mould, from which a gutta-percha cast has been taken, 

 and from this the figures and description were prepared. The specific 

 name is given in honor of Clarence King, Esq., the geologist-irt-charge 

 of the Survey of the Fortieth Parallel." (Meek.) 



Lymnaa kingii and Lymncea tenuicosta were, until recently, unique 

 among Lymnaeas, living or extinct, in the possession of strong longi- 

 tudinal ribs. Meek (op. cit. 1876) erected the subgenus Polyrhytis 

 for this species, giving the principal diagnostic character as "much like 

 the last (Radix) in form, but bearing distinct regular, vertical costae." 

 In 1884, 1 R. E. Call described a recent Lymnaa (Lymncea ampla var. 

 utahensis) from Lehi, Lake Utah, which is certainly congeneric with 

 kingii and which may well be the descendant of the Pliocene fossil, 

 having the shape of that species as well as the peculiar longitudinal 

 costse. Call's figures are not good and do not correctly represent the 

 species. A good series of kingii is a desideratum in order that com- 

 parison may be made with the recent species. 



It is thought by geologists 2 that the area of the Great Basin, in 

 Utah, has formed in ages past a huge lake (Lake Shoshone), and it 

 seems not at all unlikely that this unique Lymnaeid is the lineal ancestor 

 of Call's utahensis. 



Galba contracosta (Cooper). Plate XVII, figure 12. 



Limncea contracosta J. G. COOPER, Proc. Cal. Acad. Sci., ii, IV, p. 169, pi. 

 14, fig. 12, 1894. MERRIAM, Bull. Dept. Geol., Univ. Cal., 1, p. 363, 1896. 

 LAWSON and PALACHE, 1. c., II, p. 391, 1902. 



Limnea contracosta J. G. COOPER, Bull. Cal. State Mining Bureau, IV, p. 

 36, pi. 5, fig. 59, 1894. 



SHELL: "Form broadly ovate, whorls five, rapidly enlarging from 

 an obtuse apex, and with convex outlines to the very large body whorl, 



'Bui. U. S. Geol. Surv., no, 11, p. 47. 

 'King, Geol. 40th Parallel, Vol. I, p. 359-458. 



