84 University of California Publications in Geology [Vol. 12 



Apical system pentagonal in outline ; four large genital pores and 

 five perforated radial plates present. Petals wide ; width of each 

 poriferous zone equal to about one-half the width of the interporif- 

 erous area ; inner rows of pores diverge gradually until about one-half 

 the distance to the margin, when they converge for a short distance 

 and then diverge, continuing with rounded pores to the margin ; the 

 initial divergence of the outer rows of slit-like pores is greater than 

 that of the inner rows, and when about two-thirds the distance to the 

 margin converge close to the latter, continuing nearly to the ambitus ; 

 pores conjugated. Petals are considerably elevated near the apical 

 system, but become lower toward the margin and in some specimens 

 are nearly flush with the surface of the test in the submarginal area. 

 Odd anterior petal differs from the others in that the inner rows of 

 pores do not converge. Lower surface flat or slightly concave ; peris- 

 tome small, rounded, and slightly eccentric to the posterior, being 

 opposite the apical system. Broad, deep, straight ambulacral grooves 

 are present, which pass through the marginal notches and continue 

 on the petals as a median line or groove ; at a point slightly over one- 

 half the distance to the margin auxiliary lines are thrown off which 

 pass to the upper surface as sutural lines between the ambulacral 

 and interambulacral plates. Periproct small, round, and inframar- 

 ginal, nearly marginal. Tubereulation consists of prominent scrobic- 

 ular tubercles on the petals and ridges between the grooves on the 

 upper surface, grading into minute ones in the depressions ; those on 

 the inferior surface placed close together and nearly as large as the 

 tubercles on the petals. 



Belated forms. — Pack originally described this form as a variety 

 of Astrodapsis antiselli Conrad, calling it A. antiselli var. arnoldi. 

 Later Twitchell raised it to a species, A. arnoldi Twitchell, and in- 

 cluded under it a form previously identified by Arnold as A. whitneyi 

 Remond ; Twitchell has used the latter as his type. This was entirely 

 erroneous, as the two forms are markedly different. The writer, with 

 considerable material at hand, has deemed it advisable to retain the 

 specific rank of A. arnoldi, which according to the rules of nomencla- 

 ture takes the name Astrodapsis arnoldi (Pack). This leaves the form 

 described by Twitchell under A. arnoldi nameless. To this the writer 

 has given the name A. calif amicus Kew. 



This form differs from Astrodapsis antiselli Conrad in having rela- 

 tively narrower petals which are more elevated, a thinner margin, 

 and a less depressed test ; in having a bell-shaped profile, while that 



