2oG BULLETIN OF THE 



tical rows of small secondary tubercles. The primary tubercles of botb areas 

 are imperforate, but distinctly crenulated. At the actinostome the ambu- 

 lacra flare slightly, somewhat as in Hemicidaris. The pores are small, 

 placed in pairs far apart, one above the other, so that there seems to be, as 

 far as I could see, but a single pair of pores for each ambulacral plate, 

 though near the mouth they are somewhat closer. As in Salenia, the in- 

 dentations of the actinostome are very slight. The abactinal system covers 

 nearly the whole of the abactinal part of the test; the anal system is eccen- 

 tric. There is a marked difference in the size of the genital plates, the 

 three posterior ones being much larger than the two anterior ones ; the 

 reverse is the case of the ocular plates. In the largest genital plate there 

 is a trace of the madreporic body, corresponding to the position assigned to 

 it by Forbes, Mtiller, and Wright, and which cuts the symmetrical axis of 

 the sub-anal plate at an angle ; this is the case also with the angle made by 

 the axis of the madreporic bady and the first anal plate of young Echini ; 

 the position of the axis passing through the anal plate has no definite 

 relation to the madreporic body. The anal opening is covered by small 

 plates, as in other Echini. The whole abactinal system is studded with 

 embryonic spines, which are longest along the exterior edge of the abactinal 

 system, thus separating it most distinctly from the test. The sutures 

 between the plates are deeply cut with deep pits at the angles of junction 

 of the genital and sub-anal plate and of the ocular and genital plates. 

 The three larger genital plates have also pits in the middle of their line of 

 junction with the sub-anal plate. The genital openings are large, placed 

 in the middle of the plates. 



Off' Double Head Shot Key, 315 fathoms. 



Diadema antillarum Phil., Wieg. Archiv, 1845. 



Syn. Diadema antillarum Lutk., Bid. til Kunds. om Echin. 

 Littoral to 17 fathoms. 



Csenopedina cubensis A. Ag., nov. gen. ct sp. 



This species is a living representative of the genus Hemipedina of 

 Wright (as emended by Desor, Wright having included in it species of 

 other genera of Pseudodiadematidas). It differs from its fossil representa- 

 tive by the peculiar arrangement of the pores, which have a tendency to 

 arrange themselves in lateral arcs of three pairs. The general outline of 

 the test is that of Cyphosoma. It has, like Orthopsis, Echinopsis, Hemi- 

 pedina, perforate tubercles not crenulated. It reminds us of Pseudo- 

 diadema in having tubercles nearly of the same size, and has, like Phymo- 

 soma, only two rows of tubercles extending from pole to pole, while the 



