100 MONOGRAPH OF THE GENUS GNATHODON—DALL. vol. xvii. 



GNATHODON LECONTEI, Conrad. 

 Plate VII, Hg. 4. 



Gnathodon Lecoiiici, Conrad, Joiiru. Acad. Nat. Sci. Phila., 2d Ser., Ii, p. 273, 

 pi. 24, figs. 1-3, Jan., 1853; Proc. Acad. Nat. Sci., vii, p. 31— Gould, in Pac. 

 R. R. Rep., v.; appendix, p. 230, 18.5.5. 



Iianf)ia Lecontci, Conrad., Proc. Acad. Nat. Sci. Phila. for 1860, p. 232, 1861.— 

 Meek, S. I. Checkl. foss. N. Am., Miocene, p. 11, 1864. 



Fossil ill the upper Tertiary (Pliocene?) rocks on Carisco Creek, Col- 

 orado desert, Arizona, Dr. Lecoute. Type in the National Museum, 

 Reg. No. 6833. 



Length, 22 mm.: height, 20; diameter, 16. 



This species, which is said to occur in great abundance at the locality 

 mentioned, most nearly resembles G. cuneatus but is a more trigonal 

 shell than specimens of cuneatus of the same length, has a smaller yt\\- 

 lial sinus, and is a considerably smaller and less heavy species. There 

 are also difterences in the arrangement of teeth on the hinge line. It 

 differs from G. trigonus Petit in having long lateral teeth and in being 

 proportionately more elevated. The beaks are high and more closely 

 adjacent than in G, cuneatus. Carpenter (Kep. Brit. Assoc. Moll. W. 

 C. N. Am., 1863, p. 592) correctly distinguishes this species from G. 

 mendicus or trigonus, and recognized its greater resemblance to the 

 G. cuneatus. No specimens seem, to have been collected by any one 

 since Dr. Leconte, who described them as found in a layer of rock two 

 feet thick in the bank of the creek, where they occurred in the greatest 

 profusion. The small pallial sinus m this species is a step in the direc- 

 tion of Bangianella. 



Section MIORANGIA, Dall. 



GNATHODON .lOHNSONI, Dall. 

 Plate VII, fig. 7. 



Gnathodon Jvhnsoin, Dall, Science, Vol. xx. No. 502, p. 165, September 16, 1892 

 (name only); Trans. Wagner Inst, iii, p. 337, pi, 22, tig. 18, December, 1892. 



Fe7ius moMUana, Johnson, Science, Vol. xx, No. 501, p. 151, September 9, 1892 

 (name only). 



Fossil in the Miocene of the Pascagoula clays at Shell Bluff", Pasca- 

 goula River, Greene County, Miss.; also at a depth of 700 feet in the 

 artesian well at Biloxi, Miss., and of 735 feet in the artesian well at 

 Mobile, Ala.; L. C. Johnson. 



Shell small, rather compressed, ovate-triangular to submytiliform in 

 outline, rather thin for the genus, externally smooth or marked only 

 with lines of growth when iierfectly normal, but frequently concentri- 

 cally fluctuate owing to irregularities of growth ; beaks prominent, com- 

 pressed, anterior, close to the hinge line; margin of the shell entire, 

 with no circumscribed lunuleor escutcheon; interior smooth, muscular 

 impressions small, distinct; pallial line with a shallow incurvation 

 behind, hinge very asymmetrical, the anterior lateral tooth in the left 



