GENEEA AND GEOTJPS OF THE ECHINOIDEA. 137 



Ambulacra long, narrow, straight ; primary tubercles very 

 small, without definite order ; pairs of pores in simple series 

 abactinally, diplopodous towards the ambitus ; plates low pri- 

 maries, but possibly compound near the ambitus. 



Peristome central, decagonal, deeply incised for the branchiae. 

 Perignathic girdle present (ambulacral processes). 



Infcerradial ornamentation of many scattered rows of small 

 tubercles. Periproct supra-marginal, small, broadly ovoid, opening 

 flush. 



Fossil. Oolite : Europe. 



It is not a satisfactory genus. 



Genus Ptgastee, Agassiz, 1839, EcTi. Foss. de la Suisse, p. 79. 

 Besor, 1842, in Agass. Monogr. d'Ech. viv. et foss. livr. 3 

 p. 75. Deso7\ 1858, Synopsis, p. 164. Wright, 1856, Pal. 

 Soc. Monogr., Ech. Ool. Form. p. 273. Etallon, Ech. KauU 

 Jura, Suppl. p. 4, and Lethcea Bruntrutaiia, pi. xlv. Cotfeau 

 <Sf Triger, 1859, Ech. de la Sartlie, p. 175, pi. xxx. fig. 16. 

 Loven, 1887 (pub. 1888), Bih. till Kongl. SvensJca Vet.-Akad. 

 Handl. Bd. 13, Afd. iv. no. 10, p. 8 et seq. pi. ii. 



Test large, with a circular or pentagonal, rather shai^p ambital 

 outline ; subconical and depressed dorsally, more or less truncate 

 behind and concave actinally. 



Apical system central or slightly excentricin front, small, with 

 four perforated basal plates ; the madreporite large, in basal No. 2, 

 and extending backwards centrally, reaching the widely separated 

 posterior radial plates and the anterior edge of the periproct. 



Ambulacra straight, similar, flush or slightly raised, increasing 

 in width to the ambitus and diminishing thence to the peristome; 

 with straight narrow, simple poriferous zones ; a pair of pores 

 to a plate, but actinally there are some compound plates, and 

 some fusion of them at the peristome. Tubercles of the inter- 

 poriferous areas in two or four vertical rows, slightly smaller than 

 those of the interradia, but otherwise similar. 



Interradia very broad actinally, with low, broad, curved plates ; 

 tubercles in horizontal rows, some continuous vertically, all largest 

 actinally, very regularly placed, perforate and very slightly Gra- 

 nulate or uncrenulate, in flat or depressed areas surrounded with 

 circles, squares, or hexagons of miliaries. 



Peristome large,decagonal ; branchial incisions large, sometimes 



