156 JACKSON AND JAGGAK — STUDIES OF MELONITES MULTIPORUS. 



The ocular plates of Melonites multtporus have never been figured as 

 perforated by pores, although Meek and Worthen (30) suggested that 

 they may perhaps sometimes show pores. We have had the opportunity 

 to examine a good many ocular plates in Melonites nmltiporus, and in no 

 case were they perforated. The same observation is true of Oligoporus 

 missouriensis, Jackson.* It seems best to give up finally the idea of pores 

 in the oculars of adult Melonites, unless some are actually observed. 

 Pores in ocular plates are so constant a feature in echinoids (two are 

 figured in Palseechinus by Bailey (5)) that Melonites and Oligoporus must 

 be considered as exceptional in this feature, and quite likely they would 

 be found in the young, if such material could be obtained. 



In the figures (2, 18, 20) and tables (pages 165-170) of Melonites multi- 

 poms the several areas are oriented, the interambulacra and ambulacra 

 being designated by letters from A to J, inclusive. As madreporic plates 

 have not been seen, any interambulacral area is selected as a starting 

 point and succeeding areas are counted from left to right, revolving like 

 the hands of a watch, when looking down on the echinus from the dorsal 

 side. The orientation is necessarily reversed when the echinus is viewed 

 from the ventral side (plate 2, figure 2). It would be interesting if means 

 of differentiating areas could be established ; but at present it seems im- 

 possible, for the areas, as far as known, present no radial specializations. 

 If a definite method of orientation could be established from genital 

 plates, it is feared that this would not aid one in orienting areas in speci- 

 mens which were imperfect dorsally. Perhaps the orientation adopted 

 in these papers is as convenient as an}^ that could be practicall}' a})plied. 



Tabulations of Plate Arrangement in the interambulacral and 



AMBULACRAL ArEAS. 



In order to give a description in brief form of a greater number of in- 

 terambulacral and ambulacral areas in Melonites multiporus than could be 

 figured, the accompanying tables are introduced. Besides giving other 

 additional cases, these tables represent the arrangement in cases where it 

 would be impossible to figure them adequately, as in areas on the oppo- 

 site sides of the same specimen. 



In the tables the characters to Ije compared are arranged in perpen- 

 dicular lines. The interambulacral areas, indicated by letters A^ C, E, G 

 and /, are all considered as successive areas, as seen looking down on the 

 test from the dorsal side and revolving from left to right like the hands 

 of a watch. This is the same notation that has been pursued in the 

 plates, as plate 4, figures 18 and 19, plate 5, figure 20. The first column 



*See succeeding paper, plate 9, figure 52. 



