CLARK: THE CIDARIDAE. 191 



tudinal lamellae. Secomlary spines few, flat, and blunt, confined to scrobicular 

 circles and margins of ambulacra; latter very slender. Large globiferous pedi- 

 cellariae usually wanting ; tridentate infrequent, with slender straight valves ; small 

 globiferous abundant, on very short stalks, with prominent end-tooth on valves. 



This is a monotypic genus, closely related to the preceding but easily distin- 

 guished at a glauce by the peculiarly bare appearance of both ambulacra and 

 interambulacra. 



Chondrocidaris gigantea. 



Chondrocidaris gigantea A. Agassiz, 1863, Bull. M. C. Z., 1, p. 18. 

 Plate la, Rev. Ech., A. Agassiz, 1873. 



This species is of special interest because of its huge size (up to 95 mm. h. d.), 

 its remarkable primary spines, and its very broad median interambulacral areas 

 densely covered with minute miliaries. The color is brown of some shade, the 

 countless miliaries with a distinctly greenish-yellow cast. It is a curious fact 

 that really young specimens of gigantea have not yet been taken, none in the 

 collections of either the National Museum or the Museum of Comparative Zool- 

 ogy being less than 75 mm. h. d., and de Loriol's ('83) specimen, the smallest 

 yet recorded, was more than half that size. Most of the known specimens are 

 from the Hawaiian Islands, but it is also reported from Lifu, Loyalty Islands 

 (Bell, '99), and Mauritius (de Loriol, '83). The latter is remarkable for haviug 

 only 5 coronal plates, while Hawaiian specimens have 8-10. The record of this 

 species from the Lepar Islands, given by Sluiter ('95), is said by de Meijere 

 (:04) to rest only on spines of " C. (Stephanocidaris) bispinosa." 



DIPLOCIDAEIS. 



Diplocidaris Desor, 1854, Syn. Ech. foss., p. 45. 

 Plate 1, fig. 5, Syn. Ech. foss., Desor, 1854. 



Test much as in Phyllacanthus; coronal plates 7-8; areolae little or not at all 

 sunken, sometimes merging together actinally ; median interambulacral area not 

 sunken or bare, but with few, scattered tubercles ; ambulacra narrow, less than .25 

 of interambulacra in width; poriferous zones more or less sunken; median am- 

 bulacral are.) narrow, with usually only a single marginal row of tubercles, the 

 intervening bare space sometimes conspicuous ; pores nearly horizontal and widely 

 separated, in vertically very narrow plates, which are so crowded that they have 

 the appearance of having slipped on each other laterally, so that the pores are 

 apparently in 4 vertical series in each zone. Abaetinal system small, with large, 

 usually angular, genital and small ocular plates. Actinostome larger than abaeti- 

 nal system. Primary spines very stout, with longitudinal series of low tubercles 

 which tend to merge into ridges near the tip. Secondaries and pedicellariae ? 



This genus is very different from any living Cidaridae in the arrangement of the 

 pores, but in all other respects it is strikingly like Phyllacanthus, especially some 



