10 PROCEEDINGS OF THE NATIONAL. MUSEUM vol. 7o 



AMUSSIUM ALAZANUM, new species 



Plate 2, Figures 7, la 



Shell small, thin, suborbicular, nearly equilateral, somewhat tumid 

 medially but compressed laterally, surface smooth except for very 

 faint growth lines and G amiptonectes striations; apical angle about 

 115° ; ears large, subequal ; internal sculpture of ten strong, round, 

 threadlike ribs extending from the umbo, where they are covered 

 by a thin layer of shell, nearly to the margin and ending in flattened 

 nodes. Height, 7.8 mm. ; width, 7.6 mm. 



The length and number of internal ribs are variable. Another 

 specimen nearly the same size as the type has 11 ribs, and the ribs 

 extend only about two-thirds the distance to the margin. The distal 

 third is smooth and very thin. 



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

 Alazan (M. 49 V.) (type) and at La Ceiba Crossing, 9.8 kms. above 

 Tumbadero (M. 52 V., M. 54 V.). 



Type.—CsX. No. 352710, U.S.N.M. 



PECTEN CEIBANUS, new species 



Plate 2, Figure 8 



Right valve equilateral, moderately inflated; ribs 21, round but 

 slightly grooved distally; interspaces nearly flat, narrower than 

 ribs; submargins narrow, convex; anterior ear with about 3 riblets, 

 broken distally; byssal notch apparently shallow; posterior ear 

 oblique, with about 6 riblets; finer sculpture nearly obliterated in 

 type but traces of close-set scabrous sculpture which probably origi- 

 nally covered entire shell remain near distal margin. 



Height, 28 mm.; width, 32 mm.; diameter of right valve, 8 mm. 



Occurrence. — Oligocene, Alazan clay, Rio Buena Vista at La Ceiba 

 Crossing, 9.8 kms. above Tumbadero, Vera Cruz, Mexico. (M. 53 V.) 



Type.— C-a^t. No. 352711, U.S.N.M. 



EXPLANATION OF PLATES 



Plate 1 



I 

 Fig. 1. Oetnmula alazana Cooke 



2. Geinniula mexa Cooke 



3. Gemmula mexa Cooke (apex) 



4. Oemmula mexa var. m^exita Cooke 



5. Pseudotoma alazana Cooke 



6. Scohinella pi'ionota Cooke 



7. OlyptotomM rhombica Cooke 



8. Borsonia aguilae Cooke 



9. Ancilla (Ancillina) alazana Cooke 



10. Protonema hartschi Cooke 



11. Twritella ccibana Cooke 



12. TurHtella ccibana Cooke 



