ART. 10 NEW VICKSBURG MOLLUSKS FROM MEXICO COOKE 6 



most as many more species are represented in the available collec- 

 tions by specimens which, although good enough to identify, are 

 too imperfect to serve as types in view of the probability that more 

 and better specimens will be found in the not distant future. 



Characteristic specimens of Anadara lesuey/ri (Dall), a little ark 

 that is very abundant in the Byram marl of Mississippi and rare in 

 the Glendon formation, have been found in the Meson formation at 

 Topila, Mexico. 



The following descriptions of the localities at which the fossils 

 were obtained are based upon memoranda furnished by Doctor 

 Vaughan. 



STATIONS M. 47 V., M. 4S V., M. 49 V., CROSSING OF THE ALAZAN-MOTUTLA KOAD 



The exposures are a short distance south of (below) the road 

 crossing over the river west of Alazan. The strata are much dis- 

 turbed by minor crumpling. A thickness of 70 to 80 feet is exposed. 

 Stations 48 and 49 represent actually or nearly the same bed, which 

 is at the stratigraphically lowest part of the exposure. Station 47 is 

 probably about 25 feet higher stratigraphically than station 48. 



STATIONS M. 52 V., M. 53 V., M. 54 V., LA CEIBA CROSSING 



This locality is on the east side of Rio Buena Vista, 9.8 kms. in 

 a straight line above I'unibadero. A description of the exposure 

 follows : 



Section at La Ceiba crossing 

 Quaternary : Feet 



5. River silt, light grayish fawn colored 10 



4. Coarse gravel and cobbles at base of river deposit 2 to 4 



Unconformity. 

 Oligoceue: Alazan clay: 



3. Silty clay, originally light gray, weathers to medium fawn col- 

 ored; collection M. 52 V 4 



2. Fine to medium grained, light lead to dark fawn colored, soft 



snndstone ; grains not well rounded ; collection M. 53 V , , to 1 



1. Light lead colored clay; collection M. 54 V 1 



On the slope along the eastern side of Rio Buena Vista 50 feet 

 above the base of the exposure described above and separated from 

 it by fluvial deposits there is an outcrop of a yellowish foraminiferal 

 limestone composed largely of Lejndocyclina undosa var. tuTnida 

 Vaughan, a Meson species of Operculina, and other larger Forami- 

 nifera. As there is no indication of local faulting, it appears that 

 the foraminiferal limestone occurs stratigraphically aliout 45 feet 

 higher than bed No. 3 of the exposure on the river. Whether an 

 unconformity or disconformity intervenes between the top of the 

 Alazan and the base of the Meson can not be determined from these 



