G04 Mr. n. L. Clark on the 



wanting; abactiual end of each iuterambu- 



lacrura consists of a single large j)late adjoining 



genital; test not usually discoidal and never 



■with marginal slits or lunules. 



•Petals more or less perfect ; madreporic pores 



numerous ; size moderate to large, 15 mm. 



and up in length. (Laganid.13.) 



Genital pores present in all interradii Laganum. 



Genital pore wanting in posterior interradius. . Peronella. 

 Petals reduced and often rudimentary ; only one 

 madreporic pore ; size small, rarely up to 

 15 mm. in length. (FiBULAUiiDiE.) _ 

 Test more or less elevated, without internal 



radiating walls, except usually posteriorly, Fibidaria. 

 Test more or less flattened, with internal 



radiating walls bounding the ambulacra . . Echinocyamus. 

 Actinal ambulacral furrows distinct, at least the 

 posterior, and usually all, extending to ambitus ; 

 abactinal end of interambulacrum with the 

 usual pair of small plates adjoining genital ; 

 test commonly more or less discoidal, often 

 with marginal slits or lunules. (Scutellid^.) 

 Test without marginal slits or lunules. 



Actinal ambulacral furrows unbranched ; 

 genital pores 5 ; abactinal system very 



small Alexandria. 



Actinal ambulacral furrows more or less forked 

 or branched ; genital pores 4. 

 Petals more or less nearly closed distally . . Scidella. 

 Petals broadly open distally. 



Abactinal system at apex of test ; anus 



marginal ; petals subequal Echinarachnuts. 



Abactinal system posterior to apex of test ; 

 anus on actinal surface ; posterior 



petals much shorter than others Dendraster. 



Test with marginal slits or lunules or both. 



Not more than two marginal slits, and often 

 none, in posterior half of test-margin. 

 No lunule in posterior interambulacrum. 

 Two lunules or marginal slits present, one 



in each posterior ambulacrum EcJdnodiscus. 



Five lunules present, one in each ambu- 

 lacrum Astriclypeus. 



A lunule in posterior interambulacrum. 



Genital pores 5 Eueope. 



Genital pores 4 MelUta. 



More than eight marginal slits in posterior 



half of test-margin Hotida. 



A list of these genera^ with their types and other important 

 (lata, follows : — 



Anomolanthus, Bell, 1884. Proc. Zool. Soc. London, p. 43. Type, 

 Echinnnthus tumidus, Tenison- Woods, 1878, Proc. Linn. Soc. 

 N.S.W. ii. p. 169. Monotypic. 



Clypeaster, Lamarck, 1801. Syst. Anim. s. Vert. p. 349. Type, 

 Echinus rosaceus, Linn^, 1758, Syst. Nat. ed, 10, p. 665, = Echin- 

 ant/ius rosoceus of Gray, 18-25, A. Agassiz, 1872, et al. Type 

 iixed by elimination by Laniiirok, ISKi, Anim. s. Vert. iii. p. 13, 



