GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 105 



Localities and geologic occurence. — Upper Oligocene ; Emperador 

 limestone. Upper Limestone, Las Cascadas, Panama, D. F. Mac- 

 Donald, collector, U. S. National Museum station No. 6671, two 

 specimens, U. S. Nat. Mus. Cat. No. 324452 ; also Panama Canal Zone, 

 upper Limestone bed, near Tower " N " (opposite Las Cascadas, Gail- 

 lard Cut) D. F. MacDonald, collector, 1911, U. S. National Museum 

 station No. 5866 5, five specimens, U. S. Nat. Mus. Cat. No. 324451. 



CLYPEASTER GATUNI Jackson. 



Plate 47, fig. 1 ; plate 48, fig. 1. 

 Clypeaster gatuni Jackson, Proc. U. S. Nat. Mus., vol. 53, 1917, p. 491, pi. 

 63, fig. 1; pi. 64, fig. 1. 



This species is represented by a fine, large specimen in perfect con- 

 dition of preservation. Two additional specimens much worn and 

 incomplete are also referred to it. 



The type measures 146 mm. in length, 122 mm. in width, and 35 

 mm. in height. The test is elongate, moderately pentagonal in out- 

 line, -with slight incurving of the borders in interambulacral areas 

 1, 2, 3, and 4. Its greatest width is across ambulacra II and IV. 

 Ventrally the test is deeply concave, being flat only on the border. 

 The ambulacral petal III is equal in length to petals I and V and 

 a few millimeters longer than are petals II and IV. The petals are 

 equidistant, highly elevated, and open at their distal ends. Ventrally, 

 five deep ambulacral grooves extend to the mouth. Interambu- 

 lacra are broad on the border of the test, narrowing up dorsally and 

 very narrow near the apical disk. Each of the interambulacra 

 between the petals are strongly elevated as if pinched up. The 

 apical disk is slightly anterior to the middle of the test and is very 

 small The mouth is central, deeply sunken. The periproct is 

 ventral, slightty elliptical, its posterior border 5 mm. from' the 

 posterior limits of the test. Tubercles are small, covering the 

 dorsal surface of the test, ventrally the same, but slightly larger. 



Clypeaster ^a^n^approaches nearest, perhaps, to C. boioersi Weaver, 

 but differs in the shape of the test, the deeply concave base, the 

 shape and proportionate size of the petals and interambulacra dor- 

 sally, and the fact that the periproct is ventral instead of terminal. 



Locality and geologic occurrence. — Gatun formation, Miocene. 

 Panama Canal i ne, near Gatun Dam site, D. F. MacDonald, col- 

 lector, 1911, holotype, U. S. National Museum, station No. 5662, 

 one specimen. 



Limestone in swamp, north of Ancon Hill, about 4 miles south of 

 Diablo Ridge in the upper Oligocene Emperador limestone, U. S. 

 National Museum, station No. 6237, two specimens. 



Holotype.— Cat. No. 324453, U.S.N.M. 



This species is present on both the Atlantic and Pacific sides of 

 the Isthmus. 



