288 ECHINODERMATA— ECHINOZOA phylum iv 



uneqiial, well-developed, nearly closed. Peristome small, central, sub-circular. 

 Periproct very small, infra-marginal. Apical System central, more or less 

 pentagonal. Tertiary. 



Subgenus Ediinarachnius Leske {Dendraster Ag.). Apical system eccentric in front or 

 behind. Periproct actinal or marginal. Recent. 



Echinodiscus Leske. Like Scutella, but truncated posteriorly, and with two 

 round or «longate lunules or slits, one in each of the median lines of the 

 postero-lateral Amh. Tertiary and Eecent. 



Encope Ag. Test with a broad notch or a lunule in the median line of 

 each Amb, and a lunule in the posterior lAmh. Miocene and Recent. 



Mellita Agassiz. Test very tlat, with five or six usually closed lunules, 

 more rarely cuts ; one in the median line of the posterior lAmb, the others 

 in the Amb. Amb petaloid dorsally, the post^erior pair the longest. Pliocene 

 and Recent. 



Lenita Desor. Eocene. Ilotula Ag. (Fig. 366, g). Recent. Arachnoides 

 Leske. Pliocene and Recent. 



Suborder C. SPATANGINA Jackson. 



Ambulacral plates simple, areas commonly petaloid dorsally ; in some types pores 

 are absent in pari of the plates. Ambulacrum III often differs markedly in charader 

 from other areas. Ambulacral plates often highly specialised in form and size. 

 Primordial ambulacral plates in the basicoronal row, or (Fourtalesia) in part pushed 

 dorsally. The basicoronal plates la, IIa, Illb, IVa, Vb, are larger and with two 

 pairs of pores or two separate single pores, whereas the Ib, IIb, Illa, IVb, Va are 

 smaller with one pore-pair or one single pore. Primordial interambulacral plates in 

 the basicoronal row or (Lovenia, Pourtalesia) pushed dorsally. Base of Corona not 

 resorbed. Oculars and genitals separate, or genitals partially fused. Oculars 

 apparently absent in some Pourtalesias. Genital 5 absent, and some additional 

 genitals rarely absent. Periproct plated. Peristome eccentric, plated with non- 

 ambulacral plates only. Lantern and perignathic girdle absent (present in the young 

 of Echinoneus, A. Agassiz, 1909). No peristomal, but ambulacral gills only. 



Tribe A. CASSIDULOIDEA Duncan. 



Ambulacra abactinally petaloid or sub-petaloid, usually similar. Some or all 

 of the interambulacra with a single peristomal plafe ; the postero-lateral areas 

 symmetrical actinally, without any fusion of plates; no plastrons. Peristome 

 variously shaped, with or without floscelles. 



Family 1. Bchinoneidae Wright. 



Test toll, or low and tumid dorsally ; turaid and rarely fiat actinally. Apical 

 System central, compact, with four perforated genitals. Ambulacra similar, dorsally 

 apetalous or sub-petaloid. Pores in simple pairs or in oblique triplets actinally ; no 

 floscelle. Peristome oblique or transversely elliptical, rarely symmetrical. Periproct 

 actinal, marginal or supra-marginal. Cretaceous to Recent. 



• Subfamily A. Echinoneinae Desor. 



Test low, tumid, and more or less pulvinate actinally ; peristome central or sub- 

 central and oblique. 



