Vol. VII] DICKERSON & KEW— FAUNA MEDIAL TERTIARY 137 



and not depressed. The tuberculation consists of large primary 

 tubercles on the lateral interambulacral areas of both the upper 

 and lower surfaces, and in some specimens they are sparsely 

 present on the odd posterior interambulacrum ; large primaries 

 are lacking on the marginal area ; all are deeply scrobicular, and 

 with perforated mamelon, the latter protruding above the gen- 

 eral level of the test. Secondaries, perforated, and possessing a 

 poorly developed scrobicule ; these are situated within the area 

 surrounded by the internal fascicle, on the marginal area, on the 

 elevated portion of the odd posterior interambulacral area, 

 along the odd anterior ambulacral area, and around the peri- 

 proct and subanal areas. Milliaries are spread over the entire 

 test; these vary somewhat in size, and are irregular in their 

 distribution. Internal fasciole circumscribes a relatively large 

 area ; it is undulating, broad, and very distinct except where it 

 crosses the odd anterior ambulacral area, at which place it is 

 either absent or weakly developed. A transversely elongate 

 subanal fasciole is present. 



Geologic Horizon: — Upper Oligocene or Miocene. 



Localities:— X23, X24, X25, X62, X63 (Rio Bravo Oil 

 Company's numbers). 



Type : — No. 364, and cotypes Nos. 365 and 366, Cal. Acad. 

 Sci. 



Type Locality: — X62 (Nuevo Rancho, 35 kilometers north- 

 west of Tuxpan, near Cerro Azul. Coll., W. F. Cummins. 

 Cotype localities: X24, Salitre Ranch. Colls., Cummins and 

 Sands; X25, Salitre, one mile north. 



Named in honor of Professor E. T. Dumble. 



