GENEEA AKD GEOFPS OF THE ECHINOIDEA. 119 



Tubercles plain, and smaller and less numerous than those of 

 the interradia. 



Interradia broad at the ambitus, narrow at the peristome, with 

 several vertical rows of large plain primary tubercles. 



Peristome large, pentagonal ; branchial incisions broad. Peri- 

 gnathie girdle well developed; processes tall, with a large arch. 

 Jaw-pyramids stout, with a large tall foramen and epiphyses ; 

 teeth keeled. Actinal membrane with spine-bearing buccal 

 plates. Spines of primary tubercles moderately long, stout, 

 faintly longitudinally striated, semi-solid, becoming suddenly 

 slender and sharp, with a milled ring. 



decent. Pacific coast of Central America north to California 

 and south to Peru ; Zanzibar, Eed Sea, Mauritius, Seychelles, 

 Japan, Philippines, Sandwich Islands, Piji, Senegal coast. Cape 

 Verd, Bermudas, Caribbean Sea, Gulf of Mexico. 



Genus Stomopnetjstes, Agassiz, 1841, Monogr. JEch. viv. etfoss. 



livr. 1, Fref. p. x. A. Agassiz, 1873, Revision, p. 436. 



Martin, 1880, Bev. Foss. FJcJi. Java {Notes Leyd. Mus.). 



Stewart, 1880, Journ. Boy. Micr. Soc. vol. iii. p. 911. 



J. Bell, 1881, Proc. Zool Soc. p. 445. Fe Loriol, 1883, Fch. 



de I' He Maurice, p. 32. 

 Syn. Heliocidaris, Desm. 1846. 



Test moderate in size to very large, stout, circular or elliptical 

 in the tumid marginal outline, swollen dorsally, but depressed ; 

 actinal surface flat. The autero-posterior axis of the test is 

 oblique and forms a greater or less angle with the long diameter. 

 Apical system with a large madreporite ; basal plates form- 

 ing a narrow ring, with a secondary tubercle on each plate. 

 Periproct large, with numerous plates with small tubercles. 



Ambulacra straight, broad at the ambitus and at the peristome ; 

 poriferous zones narrow abactinally and wide actinally ; the pores 

 in arcs of three pairs dorsally, and crowded and triserial below 

 the ambitus, and interfered with nearly throughout by small 

 secondary tubercles or granules. Interporiferous areas with two 

 vertical rows of large, imperforate, plain, primary tubercles, and 

 several rows of secondary tubercles and miliaries, some entering 

 the poriferous zones, diminishing at the peristome, where the 

 areas are narrow. Spicules of the tentacles very large. 



