GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 113 



of the largest specimens measures 107 mm. in length, 103 mm. in 

 width, and 53 mm. in height. 



Locality and geologic occurrence. — Upper Oligocene. Emperador 

 limestone, Panama Canal Zone. Upper Limestone bed near Tower 

 "N" (opposite Las Cascadas, Gaillard cut), D. F. MacDonald, coir 

 lector, 1911, U. S. National Museum station No. 58666, one specimen, 

 U. S. Nat. Mus. Cat. No. 324457. Also Panama Canal Zone, from 5th 

 or topmost limestone, Gaillard cut, opposite Las Cascadas, U. S. 

 National Museum station No. 6019^, D. F. MacDonald and T. W. 

 Vaughan, collectors, 1911, 4 specimens. U. S. Nat. Mus. Cat. No. 

 324458. 



SCHIZASTER ARMIGER W. B. Clark. 



Schizaster armiger Clark and Twitcheix, Mesozoic and Cenozoic Echino- 

 dermata of the United States, Monograph U. S. Geol. Survey, vol. 54, 

 1915, p. 152, pi. 70, figs. la-d. — Jackson, Proc. U. S. Nat. Mus., vol. 

 53, 1917, p. 498. 



In this species the test is rather large, cordiform; upper surface 

 slopes at first rapidly, then more slowly from the anterior margin to 

 the apical system beyond which an elevated sharp ridge continues to 

 the truncated posterior margin. Length, 59 mm. ; width, 50 mm. ; 

 height, 25 mm. The ambulacra are broad and the odd anterior 

 ambulacra! petal III is situated in a deep groove that indents the 

 anterior margin. The two lateral anterior ambulacra II and IV are 

 in deep, broad grooves, with petals 18 mm. long. The posterior 

 ambulacra I and V, similar but shorter, are 9 mm. long. Peripetalous 

 fasciole is broad and distinct. Interambulacra gibbous, the posterior 

 No. 5 being built up into an elevated keel. The peristome is indis- 

 tinct in our specimen, but as shown in W. B. Clark's excellent figures, 

 is wide and near the anterior margin. The periproct is high on the 

 truncated posterior end. 



The type material described by Clark is ascribed to the upper 

 (Jackson) Eocene of Choctaw County, Alabama. 



Locality and geologic occurrence. — Miocene (?), x Bonilla, Costa 

 Rica, Hill collection, U. S. Nat. Mus. Cat. No. 135214, one specimen. 



SCHIZASTER CRISTATUS Jackson. 



Plate 52, figs. 2-A. 



Schizaster cristatus Jackson, Proc. U. S. Nat. Mus., vol. 58, 1917, p. 499, 

 pi. 68, figs. 2-4. 



The material of this species consists of two internal moulds ; as the 

 plates are entirely wanting, of course external characters can not be 

 given. The more perfect of the two specimens measures 40 mm. in 

 length, 36 mm. in width, and 22 mm. in height. Test is moderate 



1 According to Hill and Dall the rocks exposed at this locality are of the same age as 

 those at Gatun, Canal Zone. For a further discussion see the last chapter (by Vaughan) 

 in this volume. 



