300 TOXOPNEUSTES VAPJEGATUS. 



cellara?, and the abactinal system — agree in all specimens to a remarkable 

 degree. In the Bulletin of the Museum of Comparative Zoology, I separated 

 the genus Lytechinus from Psammechinus to which Echinus variegatm (Lam.) 

 had been referred on account of the actinal notches, the regular arrangement 

 in vertical rows of the primary tubercles, and the absence of secondary tu- 

 bercles which fill so large a space on the coronal plates of Psammechiuus 

 miliaries, as well as the arrangement of the pores and the structure of the 

 abactinal system; the arrangement of the tubercles of the test being similar 

 to that of Magnosia, from which genus it differs, however, in not having 

 tin 1 pores spreading near actinostome, but remaining trigeminate to the 

 extremity of the ambulacra, having a more deeply notched peristome, which 

 is much smaller, in comparison to the diameter of the test. Liitken, about 

 the same time, though a few weeks later, as far as publication is concerned, 

 distinguished this same genus on the same grounds which are given above, 

 and has correctly referred to it, also, E. semituberculatus from the Galapagos 

 Islands; but, as 1 have shown above, there is no good reason for separating 

 Lytechinus from Boletia, and for not restoring to both these genera their 

 original name of Toxopneustes. 



This species has. like the common Echinometra, a great geographical 

 range identical with it, but at the same time has a somewhat more ex- 

 tensive bathymetrical distribution. 



Littoral to 34 fathoms. 



In the youngest specimen ex iniined. measuring 4.7""" in diameter ( PL VI I. 

 ;'. ;). the arrangement of the pores [PL }'///. /'. & ) differed from that of the 

 adult in being in vertical rows ; the abactinal system was still quite imper- 

 fectly developed, having by no means the prominence and distinctness it 

 attains in the adult, its structure being well shown already in specimens meas- 

 uring 18.5 mm ' in diameter. In this smallest specimen the sutures of the 

 genital plates were indistinct, the ocular plates could barely be distinguished, 

 the whole anal system was covered by a large prominent plate, and on one 

 side of it, next to the left ocular plate, opened the anus; the madreporic body 

 was quite prominent, jutting out like a sponge above its genital plate. Both 

 in the ambulacra! and interambulacral areas, the two prominent rows of 

 tubercles of the adult are well marked; there are nine coronal plates; 

 buccal membrane, as in adult, covered with imbricating scales. In speci- 

 mens somewhat older, there are no important changes, beyond those of 

 the anal system, where the single plate is replaced by five, four other 



