158 PEOF. p. M. DU]SrCA.]S''s EEYISION OF THE 



Subfamily Arachn i n cd. 

 Ambulacral petals diverging ; actinal. grooves straiglit ; no 

 marginal cuts or luuules. 



Genus Arachnoides. 



Grenus Scutella, Lamarck, 1816, Hist. Nat. Anim. s. Vert. vol. iii. 

 p. 7. Agassiz, 1841, Monogr. d^Ecli. viv. et foss. livr. 2, 

 Les Scutelles, p. 75. 



Test moderate and large, much depressed, circular or sub- 

 circular in outline, or undulating slightly or notched, broadest 

 posteriorly, dorsally tumid, or subconical centrally, sloping to 

 the thin edge. 



Apical system central, more or less pentagonal ; madreporite 

 central; four genital pores at the edge of the projections ; small 

 radial plates and pores. 



Ambulacra with the petaloid parts unequal, well developed, 

 nearly closed ; poriferous zones very broad, the inner pore large, 

 the outer very small, and intermediate simple pores in the con- 

 necting groove ; actinal grooves straight and deep near the 

 peristome, bifurcating much beyond. 



Peristome central, subeircular; buccal processes projecting. 

 Jaws low, with rising laminse on either side of the superior 

 horizontal teeth ; pyramids unequal. Periproct small, infra- 

 marginal. A homogeneous ornamentation of tubercles in hexa- 

 gonal areas which are crowded with miliaries, largest actinally. 



Within the test, flat pillars and partitions, forming discontinuous 

 structures concentrically near the edge, and limiting the ambu- 

 lacra for short distances. 



Fossil. Cretaceous ? : N. America. Eocene, Miocene, and 

 Pliocene : Europe. 



Subgenus Echinaeachnitjs, Leske (genus), 1778, Acldit. ad Klein, 



p. 218. Gray, 1825, Annals of Phil. vol. x. p. 6 (genus). 



E. V. Martens, 1865 (Scutella), 3Ionatsl). d. Tconig. Akad. d. 



Wiss. Berlin, p. 140. A. Agassiz, 1872-74, Bevision, p. 315 



(subgenus). Loven, 1874, Etudes, p. 50. 



Syn. JDendraster,Kg.; Scap7iecMnus,'Ba,rjx.; Chcetodiscus,Jj\\ils.. 



Apical system excentric in front or behind. 



Ambulacral petals large, long, unequal, open or tending to close ; 



poriferous zones broad ; pores and prehensile tentacles in the 



zone between the branchial tentacles ; actinal furrows simple, 



narrow, and perforated near the peristome, bifurcating and 



