32 ECHINOIDEA. 



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

 superior, composed of tive genital and five ocular plates; madreporiform body large, 

 extending from the right antero-lateral genital plate into the centre of the disc. Vent 

 situated at the upper surface, in the margin, or at the inferior surface of the test. Spines 

 small, short, subulate. Species all extinct ; genera distributed in the Oolitic and 

 Cretaceous rocks. 



Types. Ecldnoconus alho-galerus, Klein. Tygaster seviisulcatus, Phillips. Discoidea 

 cylindrica, Lamarck. 



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

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

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

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

 oval, supra-marginal ; elements of the apical disc detached ; four genital holes. Species 

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



Types. CoUyrites ringens, DesmouHns. Collyrites ovalis, Parkinson. 



Family 8. EcHiNONiDiE. — Test thin, oval ; poriferous zones narrow, meeting at the 

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

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

 gonal, and edentulous. Vent oblong or pyriform, basal or marginal, closed by anal 

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

 another fossil in the Cretaceous rocks. 



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



Family Q. Echinobrtssid.e. — Test thin, circular, oblong, sub-pentagonal or clypeiform, 

 covered with microscopic perforate tubei'cles, 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, 

 edentulous, in general surrounded by five lobes. Vent, opening in a sulcus, in the 

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

 disc small, four genital plates ; madreporiforra body extending into the centre of the 

 disc. Species living and extinct, the latter distributed in the Oolitic, Cretaceous, and 

 Tertiary rocks, the former in the seas of New Holland, and the Antilles. 



Types. Ecliinohrissus clutiicularis, Llhwyd. Clypeus Plotii, Leske. Catopygus carinafus, 

 Goldfuss. Pygaulus cylindricus, Desor. 



Family 10. Echinolampid^. — Test thin, oblong, oval, elevated, or sub-discoidal ; 

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

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



