172 PROF. p. M. Duncan's eevistojst or the 



Genus Pyeina, JDes Moidins, 1833, Etudes sur les Ecli. p. 26. 



Agassiz,l%iO,Catal. Syst. Ectyp. Ech. Mtis. JVeoco7n.-p. 7. 



Desor, 1842, in Agass. Monogr. cVEch. viv. et fuss. livr. 3, 



p. 25. J)e Loriol, 187S, Ech. Selv. Cret. p, 201, pi. 14 ; 



1888, Faune Cret. Portug., Ech. vol. ii. fasc. 2, p. 78, pi. svi. 



Test small or moderate, ovoid, elongate, broader than higli, 



tumid at the margins and swollen abactinaliy, may be pulvinate 



actinally. 



Apical system compact, with four basal plates, the two posterior 

 radial plates close together ; madreporite large, in the large riglit 

 anterior basal plate, reaching back but only to the edge of the 

 posterior basals which are in contact ; four generative pores and 

 no fifth basal plate, or complementary plates may exist behind a 

 small madreporite. 



Ambulacra flush ; poriferous zones narrow, widely open at the 

 ambitus, apart yet closing much actinally. Pairs of pores 

 numerous, small, and separated by cost?e, non-conjugated, in 

 simple series dorsally, more or less in oblique triplets actinally ; 

 plates primaries, low and broad, with demi-plates. Interradia 

 broad. 



Peristome nearly or quite central, elongate-elliptical, slightly 

 oblique, the long axis being between zone h of amb. iii. and zone 

 a of amb. i. 



Ornamentation of both areas diffused and very equal, of sunken 

 primary tubercles, crenulate and perforate, with large and small 

 rounded granules on the intermediate structure. 



Periproct pyriform, supra-marginal, elongate, but remote from 

 tbe apical system. 



Fossil. Cretaceous: England. Cretaceous and Eocene: Eu- 

 rope. Cretaceous : N. Africa. ■ 



Subgenus Ntjcleoptgtjs, (genus) Agassiz, 1840, Catal. Syst. 

 Ectyp. Ech. Mus. Neoc. p. 7. Desor, 1842, in Agass. Monogr. 

 d'Ech. viv. etfoss. livr. 3, p. 32; Synopsis, 1858, p. 188 «. 

 Test small, circular or oblong in tumid marginal outline, de- 

 pressed, swollen above, subpulvinate actinally. 



Apical system compact, with four basal plates and five radial 

 plates all perforated, the posterior radials touch. 



Ambulacra apetalous, straight ; pairs of pores in simple series. 

 Peristome circular or elliptical, but with a decagonal outline. 



