592 NORTH AMERICAN INDEX FOSSILS. 



XX. EcHiNARACHNius Leske. 

 Differs from Scufella in its excentric apical system. Pliocenic- 

 Recent. 



30. E. gibbsi Remond. Pliocenic. 

 In outline much like Scutella fairhanksi, but larger, and apical 



system about one fourth the longitudinal diameter from the pos- 

 terior end; ambulacra broad, the transverse grooves continued 

 nearly to center; posterior petals flexuous; periproct submarginal. 

 Fernando of California. 



31. E. interlineatus Stimpson. (Fig. 1924.) Pliocenic. 

 Large (ranging to over 120 mm. in diameter), pentagonal to 



circular ; summit nearly central, in front of excentric apical system ; 



Fig. 1924. Echinarachnius interline- Fig. 1925. Ec'i'uiaraciniius excentri- 

 atus, X Yz' (After Merriam.) cus, X %• (After Merriam. ) 



posterior pair of petals shortest; anterior petal open in front, the 

 others closed ; periproct supramarginal ; ambulacral furrows dichot- 

 omise near peristome. 



Common in the Merced series of California. 



32. E. excentricus Eschscholtz. (Fig. 1925.) Pliocenic-Recent. 



Apical system excentric, one third diameter from posterior end ; 

 posterior pair of petals shortest, wide and nearly closed ; summit in 

 front of apical system. Larger than preceding. 



San Pedro of California; also Recent on Pacific coast. 



XXL MoRTONiA Desor. 

 Depressed, of medium size, more or less circular to subpenta- 

 hedral, with swollen instead of sharp borders; ambulacral petals 



