170 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Echinarachnius excentricus Eschscholtz. 



Plate XXII, Fig. 8. 



Scutella excentrica Eschscholtz, Zool. Atl., PI. XX, fig. 2, 1S26. 

 Echinarachnius excentricus Valenciennes, Voyage V^nus, PI. X, 1846. 



Though a discussion of this species is perhaps not prop- 

 erly included in a treatise on Tertiary forms, its doubtful 

 occurrence in the Pliocene is considered a warrant for its 

 introduction. Moreover, the position the species occupies 

 as the last of the Clypeastroids in this region makes 

 desirable a comparison with the extinct forms. This is 

 graphically done on Plate XXII, where E. excentricus 

 appears with its nearest allies from this Coast. 



From E. Gibbsi the excentricus differs in the less degree of eccentricity of 

 the apical system and in the greater complexity and length of the ambulacral 

 furrows. The distance of the apical shield from the posterior margin is to 

 that from the anterior margin as i to 1.8+. The ambulacral furrows are split 

 up into a great number of small branches, of which the strongest pass over 

 the margins and extend over the upper surface. Four of the strongest fur- 

 rows run to the lateral petals and stretch through their median areas almost 

 to the apical system. Those furrows not passing to the petals sometimes 

 reach half-way to the apical system. 



Quaternary, possibly also in the later Pliocene. The fos- 

 sil forms do not differ materially from those of the Recent 

 period. 



paly?50nt0l0gical laboratory, 

 University of California, 

 Berkeley, California, 

 September, 1898. 



