GENEBA. AND GKOUPS OE THE ECHINOIDEA. 107 



pair of pores, of a small demi-plate with the middle pair of pores, 

 and an aboral low, wide primary with the aboral pair of pores of 

 the triplet. Two vertical rows of well-developed primary tu- 

 bercles in the interporiferous area, and large secondaries ; some 

 of the smaller secondaries and miliaries placed around the narrow 

 depressed scrobicule of the primary tubercles, which have a large, 

 conical, distinctly crenulate boss, and the well-developed mamelon 

 is smooth and rounded. Tentacles stout and homoiopodous. 



Interradia broad, with two vertical rows of primary tubercles 

 resembling or slightly larger than those of the ambulacra, with 

 numerous secondary tubercles arranged more or less around them, 

 and miliaries ; a process actinal to each tubercle. 



All the plates of the test, except the component ambulacra! 

 plates, united by a dowelling of knobs and sockets. The trans- 

 verse sutures of all plates grooved deeply and widely, either 

 throughout their length or near the ends ; deep pits at the angles 

 of sutures and along the ambulacro-interradial sutures, under- 

 mining much of the test ; pits large, in the ambulacral median 

 line actinally and with large broad-topped spheridia. 



Peristome small, branchial incisions very small, branchiae nar- 

 row, dactylose ; actinal membrane bare, only with ten small broad 

 tentacular plates ; perignathic girdle well developed, its foramen 

 small, processes united. Pyramids of jaws with a tall foramen 

 closed above by epiphyses ; teeth keeled. Spines variable, mode- 

 rate, slender, more or less comj)ressed, striated, with a milled 

 ring, sharp or blunt at the end, especially actinally. Many 

 globiform pedicellarise with short stalks and others with long 

 stalks and long soft processes; similarly stalked small triphyllee 

 in great numbers. 



Fossil. Tertiary : Java. Mekran Series : Persian Gulf. Sub- 

 fossjl : Red Sea. 



Becent. Japan, Kamtschatka, Philippines, Arafura Sea, Mergui, 

 Ceylon, China, E. Indian Islands, Persian Grulf, New Zealand. 



Subgenus Pleueechinus, Agassiz (genus), 1841, Monogr. d'Ech. 

 viv. et foss., Pref. to Valentin, Anat. Gen. JEcJi. -p. 8. A. 

 Agassiz, 1873, Revision, p. 464 ; 1881, ' Challenger ' Beport, 

 p. 10. Martin, 1880, Bev. Foss. Ech. Java, Notes Leyd. 

 Mus. vol. ii. pp. 73-85. Duncan, 1883, Journ. Linn. Soc. 

 vol. xvi p. 447. 

 Test rather high, apical system highly ornamented, grooves of 



