Geol.— Vol. I.] MERRIAM— TERTIARY SEA-URCHINS. 169 



The distance from the eccentric apical system to the posterior margin is to 

 the distance to the anterior margin as i 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 ambulacral fur- 

 rows are well shown. On such specimens as show the lower side, the fur- 

 rows 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 Echinarachnius cxcentricus. 



The spines of the upper surface are about i mm. long; they are longitudi- 

 nally striated and at the distal end are strongly swollen and obliquely trun- 

 cated or bent. The spines of the lower surface are slender striated rods 

 about 2 to 3 mm. 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. 



Common in the Merced series. 



Genus Echinarachnius Leske. 

 Echinarachnius Gibbsi Rcmond. 



Plate XXII, Fig. 7. 



Scutella Gibbsi Remond, Proc. Cal. Acad. Sci., Vol. Ill, 1S63-67, p. 13. 

 Scutella Gibbsi. Figured by Garb, Geol. Surv. Cal., Palaeontology, Vol. II, 

 1869, p. 37, PI. XII, figs. 66 and 66a. 



Test quadrate-oval in outline. Upper surface well arched, summit behind 

 the middle of the long diameter but in front of the very eccentric apical sys- 

 tem. Specimens ranging up to 70 mm. in length. 



Petals broad, open at the ends. Posterior laterals wide apart, ovate in out- 

 line, one-half the length of the anterior pair. Anterior petal longer than the 

 anterior laterals; scattered pores continue some distance beyond the end. 



The apical shield is very eccentric. In a specimen measuring 52 mm. in 

 length, the distance from the apical shield to the posterior margin is to that 

 to the anterior margin as i to 2.18; in a specimen 70 mm. long the ratio is 

 I to 2.89. Four genital pores are present. The madreporic body is large 

 and is pentagonal in outline. The anus is inframarginal. 



The well marked ambulacral furrows are dichotomously branched near the 

 mouth-opening and send off numerous secondary branches from these forks. 

 The numerous tubercles of the upper surface are very small and are set in 

 faint pits. On the lower surfiice the tubercles are fewer in number and 

 larger, and stand in well defined pits. 



From Neocene beds near Buena Vista Lake, Kern 

 County, and listed by Ashley^ from his transition beds near 

 Santa Cruz. 



1 Proc. Cal. Acad. Sci., 2d Ser., Vol. V, 1895, p. 328. 



