ECHINOIDEA. 109 



marginal, or supramarginal. Ambulacra composed of simple 

 pores, not petaloidal. Apical disc of four perforated genital 

 plates and five ocular plates. Spines minute. No masticatory 

 apparatus. Distrib. Jurassic and Cretaceous. ///. Gen. Ana- 

 nychytes. 



2. Spatangidce (Heart-urchins). Test oval, oblong, or com- 

 monly heart-shaped, exhibiting distinct bilateral symmetry. 

 Mouth excentric. Anus posterior and supramarginal. Am- 

 bulacra petaloid, the anterior one unpaired, usually lodged in 

 a groove or " sulcus." Four genital pores. Mouth toothless. 

 Spines minute and hair-like. Distrib. Cretaceous to Recent. 

 ///. Gen. Spatangus, Micr aster, Eupatagus, Amphidetus. 



3. Cottyritidce or Dysasterida (sometimes placed with the 

 Ananchytidft) sometimes in the following order of the Echino- 

 neidce). Test circular or oval. Mouth excentric ; anus supra- 

 marginal. Ambulacra not petaloidal, meeting at two points 

 on the upper surface, which are more or less apart. Four 

 generative pores. Mouth toothless. Distrib. Oolitic and 

 Cretaceous. ///. Gen. Collyrites (Dysaster}. 



4. Echinoneidce. Test oval. Mouth nearly central; anus 

 basal or marginal. Ambulacra not petaloidal, continuous from 

 mouth to apical disc. Four generative pores. Mouth tooth- 

 less. Distrib. Cretaceous to Recent. ///. Gen. Echinoneus, 

 Pyrina. 



5. Cassidulida. Mouth central, or nearly so; anus supra- 

 marginal or infra-marginal. Ambulacra more or less petaloidal, 

 similar or dissimilar. Four generative pores. Apical disc 

 sometimes excentric. Mouth toothless. Distrib. Oolitic to 

 Recent. ///. Gen. Clypeus, Pygaulus, Pygurus. 



6. Clypeasterida. Mouth central ; anus marginal or infra- 

 marginal, posterior. Dorsal portions of the ambulacra petaloid. 

 Five genital plates surrounding the madreporiform tubercle. 

 Mouth toothed. Distrib. Cretaceous to Recent. ///. Gen. 

 Clypeaster, Scutella (fig. 59), Echinocyamus. 



7. Echinocenidce. Mouth central ; anus on the upper sur- 

 face behind, or on the lower surface, sometimes mounting so 

 high as to enter into the genital disc. Ambulacra simple, 

 narrow. Apical disc with five genital plates. Spines small. 

 Mouth toothed. Distrib. Oolitic and Cretaceous. ///. Gen. 

 Galerites (fig. 58), Echinoconus, Pygaster, Holectypus. 



8. CidaridcR. Test regular, spheroidal. Mouth central; 

 anus opposite the mouth, surrounded by the genital disc. 

 Ambulacra narrow, straight, or flexuous. Spines large, mostly 

 club-shaped. Mouth toothed. Distrib. Triassic to Recent. 

 ///. Gen. Cidaris, Temnocidaris. 



