INVERTEBRATES. 249 



Melonites and Palcechinus ; the number of its ambulacral plates 

 and pores being .only half as great as in the former, and double 

 that of the latter. It evidently approximates Melonites more 

 nearly, however, in having its ambulacra deeply furrowed, so 

 as to impart the same melon-like form to the whole outline, 

 that suggested the name Melonites. It also agrees more nearly 

 with the latter geaus, in the greater comparative breadth of its 

 ambulacra, which are about half as wide in the middle as the 

 interambulacral areas, while those of Palcechinus are only from 

 one-fifth to one-seventh as wide as the interambulacral spaces. 



It is barely possible that future discoveries may bring to ligbt other inter- 

 mediate forms, connecting Melonites and Paleechinus, through Oligoporus, by 

 such gradations as to render it necessary to include the whole as sections of one 

 genus. 



When used as a generic name, Oligoporus is less appropriate for this type than 

 when it is placed as a subgeneric name under Melonites, since it has more pores 

 than any other known type of the suborder, excepting Melonites. Another 

 objection to it is, that Desor had used the name Oligopores, in 1858, for 

 a section of the Cidaridse. As Oligopores, however, from its termination, 

 is sufficiently distinct, and many quite as unappropriate names are retained in 

 other departments of Natural History, we scarcely think it desirable to make a 

 change. If others should think differently, however, it may be called 

 Melonopsis. 



Oligoporus Dan,e, M. and W. 



PI. 17, Pig. 8. 



Melonites Danx, Meek and Wobthen, September, 1860. Proceedings Acad. Nat. Sci., 



Philad., p. 397. 

 Oligoporus , Meek and Worthen, 1860. lb., p. 474. 



Large, subglobose, or depressed ovoid. Interambulacral 

 areas lance-ovate in outline, moderately convex, occupied below 

 the middle by nine vertical ranges of plates, near the middle 

 by eight, a little higher by seven, and thus decreasing in num- 

 ber to four ranges at the highest point to which they can be 



32 Sept. 11, 1866. 



