GENERA AND GEOUPS OF THE ECHINOTDEA. 165 



Subfamily Arachnin<B (p. 158). 

 Grenus Aeachnoikes, Breyuius, 1732, Sclied. de JEch. p. 64, tab. 7. 

 figs. 7-8. Klein, 1734, Nat. Disp. EcTi. p. 33, tab. 30. 

 Agassiz, 1841, Monogr. d'EcTi. viv. etfoss. livr. 2,.Les Scutelles, 

 p. 94. Gray, 1851, Cat. Bee. Ecli. Brit. Mus. pt. i. p. 13. 

 A. Agassiz, 1873, Bevision, p. 528. Loven, 1874, Etudes, p. 34. 



Syn. Astewdaspis, Conrad; Alexandria, Pfeffer, 1880 (?). 



Test thin, very depressed, outline circular, edge thin, slightly 

 subcorneal dorsally. 



Apical system central, tumid, the madreporite surrounded by 

 radial plates and four or five genital pores. 



Ambulacra very large, greatly exceeding the interradia in area, 

 the petaloid portion with, narrow poriferous zones very widely 

 divergent and open distally ; plates of petaloid part compound, 

 an aboral demi-plate and a large adoral primary plate ; the trans- 

 verse sutures riddled with minute pores ; actinally the plates form 

 the whole of the peristomial margin or not ; the ambulacral 

 grooves straight, perforated by two buccal pores; with or with- 

 out a process passing over the margin ; and reaching the apex, 

 imperforate. Two spheridia to each ambulacra! groove near the 

 peristome, hidden. 



luterradia small, narrow apically, ending there with, two plates, 

 excluded from the peristome or not ; not perforated by pores. 



Peristome subpentagonal, central. 



Jaws flat, with a crest and small rotulse ; teeth superior. The 

 perignathic processes are stout, moderately tall and bent; there 

 are two placed side by side on each peristomial interradial plate. 



Periproct abactinal, near the posterior margin, small, circular. 

 Tubercles of the ambulacra in oblique series ; interradial tuber- 

 culation coarse, irregular, largest and least crowded actinally. 



The internal structure of the test shows concentric rows of 

 disconnected calcareous walls or calcareous pillars near the inner 

 edge, branching and stellate nearer the middle of the test ; neither 

 partitions limiting the ambulacra near the margin, nor hard 

 structures separating the ambulacral and intestinal areas. 



Fossil. Pliocene : California. 



Becent. Amboyna, N. Australia, Plinders Is., New Zealand, 

 East Indian Islands, Burmah, Mergni. 



^/e^«wJn«, Pfeffer, 1880, Verhandl. d. nat. Vereins. v. Hamb.- 

 Altona, n. P. v. p. 63, appears to be an Araclinoides with a pos- 

 terior notch. 



