1920] Keiv: Cretaceous and Cemzoic Echinoidm 



63 



5.0 mm. Outline varies from siibcircular to suboval or subovate ; 

 ambitus broadly and deeply notched in the two posterior ambulacral 

 areas, so that a lobe-like appearance is given to the posterior portion 

 of the test ; very slightly notched in the anterior ambulacral areas ; 

 greatest lateral diameter posterior to the center of the test. Upper 

 surface much more depressed in the posterior than in the anterior 

 part ; rises from a very thin edge to a low pointed apex which is 

 situated slightly anterior to the center of the test ; profile from 

 margin to summit is usually somewhat concave. Apical system eccen- 

 tric to the anterior, and in most specimens coincides with the apex 

 of the test, though it may be posterior to the latter. Madreporie 

 area large and subpentagonal in outline ; four large genital pores 

 present. Five small perforated radial plates are situated at the base 

 of the petals. Ambulacra considerably wider than the interambulacra 

 at the ambitus. Petals of moderate size and extending about two- 

 thirds the distance from the the apical system to the margin ; petals 

 of the bivium slightly longer than the others, with the odd anterior 

 one the shortest ; rows of pores regularly curved, giving them a sub- 

 lanceolate appearance ; pores converge but little in the distal ends of 

 the petals ; odd anterior petal wide open and broader than the others. 

 Poriferous areas relatively broad, being about two-thirds the width 

 of the interporiferous area. Outer rows of pores slit-like in outline ; 

 inner rows smaller and suboval. Poriferous areas somewhat sunken 

 below the general level of the test. Anterior median portion of the 

 abactinal surface longitudinally and broadly ridged, the elevation ex- 

 tending back into the odd posterior interambulacra! area ; interporif- 

 erous areas of the lateral petals slightly elevated. Inferior surface 

 very slightly concave. Peristome anteriorly eccentric, relatively large, 

 and subcircular in outline. Ambulacral furrows are broad, indistinct 

 grooves extending to the edge of the test. Periproct large, round, 

 and supramarginal, though in some specimens it is nearly marginal. 

 Tubercles small, numerous, and of the same size on both surfaces. 



Related forms. — From Scutella merriami (F. M. Anderson) this 

 form differs in that the periproct is supramarginal or marginal instead 

 of being inframarginal ; that it has a much thinner test, and lacks the 

 swollen margin ; that the notching of the ambitus in the ambulacral 

 areas is greater ; and that the poriferous areas are relatively narrower. 

 These forms are closely related and may be confused due to their 

 similarity in size and in that the raised odd anterior petal is common 

 to both. From 8. tejonensis Kew it may be readily distinguished by 



