82 University of California Puhlications in Geology [Vol.12 



ambulacral areas in some specimens. Apical system sunken, central 

 to slightly subcentral, and coinciding with the summit ; madreporic 

 area pentagonal ; four oval genital pores present, the odd posterior 

 one being absent ; five perforated radial plates are situated at the base 

 of the petals. Ambulacra one and a-half times the width of the inter- 

 ambulacra at the margin. Ambulacral ai^eas petaloid. Petals of 

 moderate width and extending close to the edge of the test ; poriferous 

 areas very narrow, with correspondingly wide interporiferous area. 

 Odd anterior petal somewliat narrower than the lateral petals. Inner 

 rows of pores round, not converging toward their extremities ; outer 

 rows of pores transversely elongate and converging close to the inner 

 rows when about half the distance to the margin, from which point 

 both rows continue in nearly parallel lines to the margin, the double 

 rows diverging from each other when about three-fourths the distance 

 to the margin. Pores conjugated. Petals elevated above the general 

 surface of the test. Interambulacral areas grooved from the apical 

 system to tlie margin ; secondary grooves faintly present along the 

 sides of the petals in the ambulacral areas, which together with the 

 interambulacral depressions form two triangular facets on the surface 

 of the test between the petals. Inferior surface slightly concave. 

 Main ambulacral grooves are straight, broad, and deep near the peris- 

 tome, and continue over the edge on the upper surface, forming a 

 median line on the petals ; the suture between the ambulacral and 

 interambulacral areas is marked by a broad, distinct line on both 

 upper and lower surfaces. Peristome central, large, and circular to 

 subpentagonal in outline. Periproct large, round, inframarginal, and 

 situated near the edge of the test. Tubereulation prominent, consist- 

 ing of rather large, scrobicular tubercles, which are the same size on 

 both surfaces, except on the depressed portions of the test and in the 

 ambulacral area near the peristome, where they are somewhat smaller ; 

 not crowded, but more numerous on the under side. Internal struc- 

 ture consists of heavy radial partitions which reach from the roof to 

 the floor and extend from the inside edge about one-fourth the dis- 

 tance toward the center ; disconnected concentric ridges are present 

 in the spaces between the double rows of radial partitions; the re- 

 mainder of the floor is more or less roughened. 



Related forms. — This species differs from Astrodapsis tumidus 

 Kemond, which it most closely resembles, in that the interambulacral 

 grooves are shallower, that it has a thicker but relatively more de- 

 pressed test, less elevated petals, and less numerous but more promi- 



