20 NATURAL FAMILIES. 



peristome notched, dividing the circumference into ten nearly equal lobes. Apical disc 

 central, superior, composed of five genital and five ocular plates ; the madreporiform body 

 being large, and extending from the right antero-lateral genital plate into the centre of 

 the disc. Anal opening situated at the upper surface, in the margin, or at the inferior 

 surface of the test. Spines small, short, subulate. The species are all extinct ; the genera 

 are distributed in the Oolitic and Cretaceous rocks. 



Types. Echinoconus albo-galerus, Klein. Pygaster semi-sulcatus, Phillips (PI. XVII). 

 Holectypus depressus, Leske. 



Family 7. CollyritidvE. — Test thin, circular, or oval ; ambulacral areas meeting at two 

 points on the upper surface, which are more or less apart ; poriferous zones narrow, pores 

 unigeminal ; tubercles small, numerous, perforated, and crenulated. Mouth opening ex- 

 central, small, round, oval ; peristome feebly fissured ; jaws unknown. Anus round, oval, 

 supra-marginal ; elements of the apical disc detached ; four genital holes. The species 

 are all extinct, and distributed in the Oolitic and Cretaceous rocks. 



Types. Collyrites ringens, Desmoulins. CoUyrltes ovalis, Parkinson. 



Family 8. Echinonid^e. — Test thin, oval ; poriferous zones narrow, meeting at the 

 apical disc ; pores unigeminal ; tubercles of both areas nearly equal, but neither perforated 

 nor crenulated ; spines stout, subulate. Mouth opening nearly central, irregularly penta- 

 gonal, and edentulous. Anal opening oblong or pyriform, basal or marginal, closed by 

 anal plates ; apical disc nearly central ; four genital pores. One group is living in tropical 

 seas j another is found fossil in the Cretaceous rocks. 



Types. Echinoneus cyclostomus, Leske. Pyrina Desmoulinsii, D'Archiac. 



Family §. EcHiNOBRissiDiE. — Test thin, circular, oblong, sub-pentagonal or clypeiform, 

 covered with small tubercles, surrounded by excavated areolas; ambulacra narrow, 

 enclosed by poriferous zones, more or less petaloidal ; pores set at different distances apart, 

 and united by connecting sutures. Mouth opening small, nearly central, pentagonal, 

 and edentulous, in general surrounded by five lobes. Anal opening, lodged in a sulcus, in 

 the upper surface of the single inter-ambulacrum, or in a marginal depression thereof ; 

 apical disc small, four genital lobes ; madreporiform body extending into the centre of the 

 disc. One species is living, the others are all extinct, and distributed in the Oolitic, 

 Cretaceous, and Tertiary rocks. 



Types. Echinobrissus clunicularis, Llhwyd. Clypeus sinuatus, Leske. Catopyus 

 carinatus, Goldfuss. Pygaulm cylindricus, Desor. 



Family 10. Echinola.mpid,e. — Test thin, oblong, oval, elevated or sub-discoidal ; 

 ambulacra large, petaloid ; poriferous zones wide ; pores placed apart, and united by a 

 suture ; the zones extend near to the margin. Mouth small, surrounded by five lobes, 



