526 ECHINARACHNIUS MIRABIL1S. 



between the ambulacra! furrows and their ramifications, decreasing but little 

 in size towards the edge of the test in the posterior half of the actinal sur- 

 face, while in the anterior half they arc much smaller and more closely 

 packed, arranged like those of the upper side. The spines of the upper 

 surface are slightly club-shaped, short ; those of the lower sides are longer, 

 more slender. The color when alive is of a grayish-green both above end 

 below. 



The calcareous partition walls and pillars connecting the two floors are 

 quite indistinct near the edge of the test, forming a nearly solid edge, with 

 but lew narrow parallel and diverging channels ; towards the centre they 

 become distinct, but are more numerous than in either of the other two species 

 of the genus, leaving but a narrow median ambulacra! space free. The 

 interambulacral pillars extend half the distance from the edge to the apical 

 system both in the odd posterior and posterior lateral ambulacral regions, and 

 half-way to the vertex in the anterior interambulacral spaces. 'Hie grooving 

 of the lower floor by low ridges running at light angles to the ambulacral 

 tube is very prominent, while the similar sculpture of the lower floor of E. 

 parma ami E. mirabilis is noi very prominent. The auricles are low but 

 strong, and connected at their base by a broad ridge running round the v<}\sc 

 of the actinostome, which in the other species of the genus is scarcely ap- 

 parent. The anus is placed at a distance of one and a half to three times 

 its diameter from the posterior edge. 



California ; Kamtschatka. 



Echinarachnius mirabilis 



! Scaphechinus mirabilis Barv , 1S(53. in. A. Ac, Proc. A. N. S. Pltila., p. 359. 

 \ Echinarachnius mirabilis A. A<;.. is;-.'. Rev. Ech., Pt. I. p. 107. 



PL Xlir.f. 5-e; PI XXXVII. f. 7, 8. 



Outline from above pentagonal, with rounded angles anteriorly, while the 

 two sides of the pentagon forming the posterior interambulacral space, at the 

 angle of which the anus is placed, form a sharper angle ; the median ambulacral . 

 spaces somewhat re-entering aiong the edge of the test, especially the two 



