4 PROCEEDINGS OF THE NATIONAL, MUSEUM vol. 73 



exposures, but exposures elsewhere suggest stratigraphic gradation 

 without the intervention of an erosion interval. As the Meson is at 

 least approximately the equivalent of the Glendon formation of the 

 eastern Gulf States, the stratigraphy indicates that the typical 

 Alazan corresponds to a part of the Oligocene older than the 

 Glendon. 



DESCRIPTION OF SPECIES 

 GEMMULA ALAZANA. new specie! 



Plate 1, Figure 1 



Shell polished, apical angle about 28° ; nucleus of four or five 

 convex whorls, the first two apparently smooth, others with close-set 

 axial costae; later whorls carinated, carina very slightly anterior to 

 the middle, crenulated ; posterior slope concave, with one spiral thread 

 close to the suture and several very faint threads; anterior slope 

 slightly concave, steeper, with several threads of variable fineness 

 and one coarser thread adjacent to the suture; anterior end of body 

 whorl with two coarse threads and many finer threads; aperture 

 about one-third the length of the shell ; canal straight ; anal sinus at 

 the carina; inner lip enameled. Length of specimen with six and 

 one-half postnuclear whorls, 15 mm. ; breadth, 6.1 mm. 



Gerrmmla al<JjZObna closely resembles G. mexa^ but is more slender, 

 lacks the double threads on the carina, and has a shorter nucleus. 



Occurrence. — Oligocene, Alazan clay, Rio Buena Vista, west of 

 Alazan, Mexico. (M. 49 V.) 



Type.— C2it. No. 352695, U.S.N.M. 



GEMMULA MEXA, new species 



Plate 1, Figures 2, 3 



Shell polished, apical angle about 35° ; nucleus of five and one-half 

 or six convex whorls, the first two very small, smooth, others deco- 

 rated with close-set axial costae; later whorls carinated; carina 

 slightly anterior to the middle, crenulated, with two adjacent nodular 

 threads, the posterior threads somewhat more strongly nodular than 

 the other; posterior slope concave, with a faint thread near the 

 suture; anterior slope concave; anal sinus deeply reentrant at the 

 carina. Body whorl broken in type; in very young shells the canal 

 is short and straight, and the anterior end of the body whorl is set 

 with spiral threads. Length of nucleus and five and one-fourth sub- 

 sequent whorls, measured to carina, 8.6 mm.; maximum diameter, 

 6 mm. 



Occurrence. — Oligocene, Alazan clay, Rio Buena Vista west of 

 Alazan. (M. 49 V.) 



Type.—CBi. No. 352693, U.S.N.M. 



