Vol. VII] DICKERSON & KEW— FAUNA MEDIAL TERTIARY 135 



the odd ambulacrum one-half the width of the opposite ones; 

 odd posterior interambulacrum slightly narrower than the pos- 

 terior lateral pair. Lateral ambulacra petaloid ; pores attain 

 their maximum divergence rapidly, and then continue in par- 

 allel lines, the rows extending about seven-tenths the distance 

 from the apical system to the ambitus ; posterior pair of petals 

 diverge from each other in curving lines; anterior pair curve 

 forward, the degree of curving being greater within the last 

 half of their length. Interporiferous area equal to each porif- 

 erous area. Petals semi-flush with the surface of the test. 

 Pores large and oval in outline; those close to the apical sys- 

 tem, very small and undeveloped. Pores of lateral petals ex- 

 tend beyond their extremities and continue irregularly to the 

 peristome. Odd anterior ambulacrum possesses a very small 

 pair of pores in each plate, this character extending from the 

 apical system to the peristome. Apical system excentric to 

 the anterior of the center of the test; is very small and con- 

 tains four relatively large genital pores, crowded together. 

 Upper surface of test arching slightly and with interporiferous 

 areas somewhat raised above the surface; apical system de- 

 pressed. Inferior surface slightly convex; peristome situated 

 near the anterior margin, large, crescent-shaped and with 

 prominent labrum which is followed posteriorly by a low 

 broad amphisternum. Periproct situated on the posterior 

 truncation of the test, and is larger than the peristome; out- 

 line subcircular, but with transverse diameter slightly greater 

 than the anteroposterior diameter. Tuberculation consists of 

 a few large primaries on the interradial areas and medium 

 sized tubercles crowded together on the under surface. Peri- 

 petalous and subanal fascioles present. The finer features can 

 not be distinguished on this specimen, due to weathering. 



This species may be distinguished from other forms of 

 Macropneustes by the curving of the petals. 



Geologic Horizon: — Upper Oligocene or Lower Miocene. 



Type:— No. 375, Cal. Acad. Sci. 



Type Locality: — MX-130 (Rio Bravo Oil Company's num- 

 ber), hill at extreme north end of La Puerte Range, Topila, 

 Mexico. Coll., Mr. Muir. 



