CIONOBRISSUS. 221 



kinds; one coarse and heavy like the rostrate, but the valves, about .65 mm. 

 long, are nearly straight and are pointed; the other has narrow, straight, com- 

 pressed valves, about half a millimeter long, the blade with serrate margins. 



Meoma ventricosa. 



Spatangus ventricosus Lamarck, 1816. Anim. s. Vert., 3, p. 29. 

 Meoma ventricosa Lutken, 1864. Vid. Med. f. 1863, p. 120. 



This is the West Indian species of the genus, ranging from Honduras to 

 Guadeloupe. The pedicellariae are abundant and quite diversified, but neither 

 globiferous nor ophicephalous could be found. A few triphyllous with trowel- 

 shaped valves, like those of Spatangus, measuring .12 mm. in length, were seen 

 but they appear to be quite rare. The tridentate are of two kinds. The smaller 

 have the valves about half a millimeter long, rather slender but widened distal 

 to middle and a little compressed at base of blade; the margins are nearly entire 

 basally but distally where the valves meet each other, the margins are finely 

 serrate. The large tridentate are quite characteristic; the valves are .75- 

 2.20 mm. long with very coarsely and irregularly serrate or dentate margins; 

 the largest ones are distinctly compressed basally and more or less abruptly 

 expanded near tip where they meet. The rostrate pedicellariae also occur in 

 two forms. In one, the valves are very strongly curved, measuring about 

 25% more along the arc than on the chord; on the chord they are .40-85 mm. 

 in length; they are very coarse and stout as in grandis. The other form has 

 the valves nearly straight, rather more flattened and measuring about 1.10 mm. 

 long, .40-.45 mm, across the base, .12-. 15 mm. across the blade near its base 

 and .20-.25 mm. across the blade near tip. On the whole the pedicellariae of 

 ventricosa are quite distinctive and help to separate the species from its ally 

 from the western coast of Mexico. 



Cionobrissus. 



A. Agassiz, 1879. Proc. Amer. Acad., 14, p. 206. 

 Type, Cionobrissus revinclus A. Agassiz, 1879, loc. cit. 



Examination of a cotype of the only species in this genus, taken near the 

 Aru Islands in 800 fms., by the Challenger, reveals only a single kind of 

 pedicellariae. This may be called either tridentate or triphyllous; the stalk 

 is about a millimeter long, the neck one third as much more and the valves 

 about .20 mm. There is nothing distinctive to be noted in any feature. 



