PLIOCENE ECHLNODERMATA. 217 



Ambulacra rather broad, of unequal length, anterior three of about the same length and longer than the posterior 

 pail-. Anterior petal open at the end, the others nearly closed. Few if any pores continuing beyond the ends of the 

 petals. 



The distance from the excentric apical system to the posterior margin is to the distance to the anterior margin as 

 1 to 1.5. The anus is supramarginal, being separated from the margin in adult specimens by about the width of one 

 of the marginal interambulacral plates. 



No specimens have been seen by the writer in which the ambulacra! furrows are well shown. On such specimens 

 as show the lower side, the furrows seem to be dichotomously divided near the mouth. This agrees with Remond's 

 description, which also states that the furrows are not as well marked nor as much branched as in Dendraster excantricus. 



The spines of the upper surface are about 1 millimeter long; they are longitudinally striated and at the distal 

 end are strongly swollen and obliquely truncated or bent. The spines of the lower surface are slender striated rods 

 about 2 to 3 millimeters long. The tubercles differ little in size on the upper and lower surfaces. 



The internal skeleton comprises numerous irregular pillars and plates near the margin and a pair of radial plates in 

 each interambulacral space. 



Dimensions. — The specimens vary from small to large, ranging, according to Merriam, up 

 to 120 millimeters in diameter. The specimen figured gave: Length 56 millimeters; width 56 

 millimeters; height 5 millimeters. 



Related forms. — D. interlineatus is very closely related to D. oregonensis. There appear to 

 be differences, however, which justify the separation of the two forms, to judge from the speci- 

 mens studied. D. oregonensis is to be distinguished by the details of its ambulacral petals. In 

 both the anterior and posterior paired petals the posterior poriferous zones are straight, while in 

 D. interlineatus all are curving, or at most only the posterior zones of the posterior pair become 

 nearly straight. In D. oregonensis all of the petals are well open at the ends, the poriferous zones 

 converging slightly or not at all toward the ends and diverging sharply at the ends, with several 

 pairs of pores occurring between the ends of the petals and the margin; while one of the most 

 striking characters of D. interlineatus is the curving around abruptly toward each other of the 

 poriferous zones so as to practically close the petals in all but the anterior petal . D. oregonensis 

 differs further in having less symmetrically subelliptical petals, in being relatively higher in 

 proportion to its width, and in having a relatively larger periproct. 



D. interlineatus also resembles S.fairbanksi and S. gabbi; but both of these forms can be 

 easily distinguished by the central or slightly anteriorly excentric jDOsition of their apical systems, 

 their relatively smaller and more equal petals, and their wider marginal areas. 



Locality. — In the sea cliffs about one-fourth mile above Mussel Rock (figured specimen) ; 

 south of Point Lobos, near San Francisco (type) ; Ano Nuevo Creek, near Felt Lake and in the 

 sea cliffs between Santa Cruz and Capitola, and at Rio Dell Diller, Cal. (Arnold). 



Geologic horizon. — Merced formation, upper Pliocene. 



Collections. — U. S. National Museum; University of California (19427). 



Genus ASTRODAPSIS Conrad. 

 ASTKODAPSIS FERNANDOENSIS Pack. 



Plate CI, figures 1, 2. 



Astrodapsis fernandoensis Pack, 1909, California Univ. Dept. Geology Bull., vol. 5, No. 18, p. 279, PL XXIV, figs. 3, 4. 

 Astrodapsis fernandoensis Stefanini, 1911, Soc. geol. italiana Boll., vol. 30, p. 706. 



Description. — As the writer has had no opportunity to study any specimens of this species, 

 the description of Pack will be given in full. 



Test small; suboval in outline, anterior end rounded, posterior end slightly pointed; much depressed, upper 

 surface very slightly convex, apex central; edges rounded. Apical system central; petals extend to margin, wide 

 open at the end, raised near the apical system but almost flush with the surface of the test near the margin. Poriferous 

 zones very narrow, together forming about one-fourth the width of the petal. The two posterior petals are gently 

 convex toward the median line through the posterior interambulacral space. A broad, shallow depression occupies 

 the center of the interambulacral areas; the two secondary depressions so prominent in Astrodapsis antiselli are almost 

 entirely lacking. Actinal surface gently concave, furrows poorly marked, but apparently branched as in Astrodapsis 

 antiselli. Anal pore submarginal, large, and oval in outline. The posterior end of the test is produced beyond the pore 

 to a small point, particularly noticeable in the smaller specimens. Tubercles very large, and set in well-defined pits 

 apparently the same on upper and lower surfaces. 



