ECHINARACHNIUS. 



SCUTELLIDAE. 



Family Scutellidae Agass. 1S41. Mon. Scut, (emend.) 



(SCUTELLA.) Echinarachnius. 



Echinarachnius Lf.ske 1778. Klein Add. 



Outline circular, test thick ; ambulacral petals large, very distinct, open at 

 extremity. Ambulacral furrows sending ramifications out only once near 

 marginal extremity. Mouth central, anus marginal or rather supra-marginal. 

 This genus differs externally from Scutella merely by the position of the 

 anus and the mode of ramification of the ambulacral furrows of the actinal 

 surface, — the median furrow, like that of Laganum, being preserved to the 

 edge of the disk, — and it would perhaps be natural to consider it simply as a 

 subgenus of Scutella, as proposed by Martens. An examination of the inte- 

 rior shows that it has the same arrangement of pillars as Dendraster and Sca- 

 phechinus. The mere eccentricity of the apex and the slightly different mode 

 of branching in Dendraster do not entitle it to rank even as a subgenus of 

 Scutella; in Echinarachnius, Dendraster, and Scaphechinus the pillars of the 

 interior are more or less concentric with the edge {PI. XI d . f. 4, 5), while in 

 Scutella they recall more the stellate arrangement of Mellita. The ambu- 

 lacral notches of the posterior extremity of Scutella are more or less present 

 in all the genera, so that externally Scaphechinus and Dendraster do not 

 differ from Scutella, the position of the anus being of no value, while inter- 

 nally they show a somewhat different arrangement of the pillars of the 

 edge of the test. For this reason I am inclined to consider Echinarachnius 

 as a subgenus of Scutella ; with it Dendraster and Scaphechinus will be 

 merged as mere sections. 



The jaws are high, supported upon feeble auricles, lobed in the centre ; the 

 teeth are not enamelled at the tip ; the edges of the triangular base of the 

 jaws form at their junction a prominent projection, formed of elliptical or 

 circular cells, rising far above the level of the jaws, instead of the lamellar 

 structure of the edge of the jaw existing in Clypeaster, Mellita, and Encope. 



