138 JACKSON AND JAGGAR — STUDIES OF MELONITES MULTIPORUS. 



Hambach, which shows numerous spines. In the description it is stated 

 that the ambulacral areas are covered with little spines about one-eighth 

 of an inch in length, while the spines of the interambulacra are only one- 

 half as long. This peculiarity Professor Hambach refers to as one of the 

 points of specific distinction from Melonites multljwras, which indicates 

 that he was familiar with the spines of that species. This distinction of 

 the two species is noteworthy, inasmuch as M'Coy's (29) distinction of his 

 family of the Palseechinoidea is based largely on the uniformity of the 

 spines as distinguished from the two series present in the Archa30cida- 

 ridse. As stated above, only a very few spines of the interambulacra of 

 Melonites multl'porus were found of the same lenojth as those in the am- 

 bulacra. It is possible, therefore, that in Professor Hambach 's specimen 

 of Melonites crassus all the spines of the interambulacra were so eroded as 

 to give the impression that they were really shorter than those of the 

 ambulacra. This could easily happen, and it is the only species of the 

 Melonitidae in which such a difference is noted. 



Besides the foregoing, the spines of American Melonitidie have been 

 described by Messrs Miller and Gurley (34) in Melonites indianensis, 

 Miller and Gurley, and Oligoporus belliUus, Miller and Gurley. In the 

 succeeding paper the spines of Oligoporus dance are described (plate 6, 

 figure 32). 



Arrangement and Development of the ambulacral and interam- 



BULACRAL PlATES. 



The next subject to which attention is called is the regular arrange- 

 ment and method of introduction of the plates of the ambulacral and 

 interambulacral areas in the Melonitida^. The arrangement of the inter- 

 ambulacra has been partially figured in Oligoporus danx, M. and W., and 

 appears fragmentarily in a number of published figures of Melonites, Pa- 

 Ixechinus, and some other genera of Pala^echinoidea, but its significance 

 and true relations seem to have been quite overlooked. 



Roemer (36) supposed that the intercalated columns terminated in 

 much the same way at either end. He says : " Die Vermehrung dcr Reihen 

 von den Polen gegen die Mitte der Schale hin geschieht durch allmiih- 

 liches Einsetzen neuer Reihen zwischen die vorhandenen." 



Loven (25) says of the Perischoechinoida that the adambulacral plates 

 alone extend from the peristome to the dorsal pole, which observation is 

 entirely supported by the results of our studies. 



Miller and Gurley (34) consider briefly the method of growth of Oligo- 

 porus blairi, Miller and Gurley. They express tentatively the belief that 

 the number of columns of interambulacral plates does not increase with 



