TERMINOLOGY. 33 



Vent transversely oblong, and infra-marginal ; apical disc small, excentral, with four 

 genital holes. Some species are now living in warm seas, but the greatest number are 

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



Types. Conodypus Leskei, Goldfuss. Echinolampas orientalis, Gray. Pygurus 

 Koeniyi, Gray. 



Family W. Clypeasterid^. — Test thick, elevated or depressed, circular, elliptical, or 

 pentagonal; surface closely covered with small, nearly equal-sized tubercles, sunk in 

 the plates, and surrounded by ring- like areolas, tubercles carrying short hair-like spines. 

 Mouth large, central, and pentagonal, armed with five strong jaws, containing the 

 same number of teeth. Vent posterior, marginal or infra-marginal ; interior of the 

 test divided by pillar-like processes, formed of the inner layer of the plates. The dorsal 

 portions of the ambulacral areas have a petaloid form, circumscribed by large poriferous 

 zones ; the basal portions are narrow, rectilineal, or branched ; the five genital 

 plates form a circle round the madreporiform body, and between these are wedged the 

 five ocular plates. This family includes the genera Cli/peaster, Lamk., Layanum, Klein, 

 Echinarachnius, Van Phels., Araclmoides, Klein, Scutella, Lamk., Bendraster, Agass., 

 Lobophora, Agass., Encope, Agass., Echinodiscus, Breynius, Mellita, Klein, Buna, Agass., 

 Moulinda, Agass., ScuteUina, Agass., Echhiocyamus, Van Phels., Fibularia, Lamk., 

 Lenita, Desor. 



Types. Clypeader rosaceus, Lamarck. Scutella suhrotunda, Lamarck. Ecldnarach- 

 nius placenta, Gmelin. 



Family 12. EcHiNOcoRiDiE. — Test thick, oval or cordate, and sometimes conoidal; 

 ambulacral areas contracted ; poriferous zones narrow, pores unigeminal ; test covered with 

 small perforated and crenulated tubercles. Mouth small, excentral, tranversely oblong. 

 Vent nearly of the same size, oblong, marginal or supra-marginal. Apical disc elongated, 

 nearly central, with four genital pores ; the cordate forms have an anterior central depres- 

 sion, and one genus has a marginal fasciole. The species are all extinct, and limited to 

 the Cretaceous rocks. 



Types. Echinocorys vulyaris, Breynius. Ilulaster subglobosus, Leske. Cardiaster 

 granulosus, Goldfuss. 



Family 13. Spatangid^. — Test thin, oval, oblong or cordiform, exhibiting the bila- 

 teral symmetry of the Echinoidea. Vent posterior and supra-marginal, closed by a com- 

 phcated series of small plates. Apices of the ambulacral areas united at the summit of 

 the test. The single ambulacrum has a different structure from the antero- and postero- 

 lateral pairs, and is lodged in general in a depression of the test, which extends to the 

 anterior border, and forms the anteal sulcus; test extremely thin, and covered with 

 small tubercles, which support hair-hke spines. Besides these there are some larger 



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