MICROCYPHUS ZIGZAG. 469 



Microcyphus zigzag 



! Microcyphus zigzag Agass., 184G, C. R. Ann. Sc. Nat. VI. 



pi vnr.f. ii-is. 



The young only of this species was described in the Catalogue Raisonne, 

 small specimens measuring about 12 uml in diameter and H mm - in height. 

 The outline from above is but slightly pentagonal ; test moderately stout ; a 

 few spines only preserved, similar to those of Amblypneustes, but somewhat 

 longer. Outline of test is more globular than the corresponding stages of 

 M. maculatus. The number of coronal plates is larger, the outline of this 

 species, especially of larger specimens, recalling more the ovoid Ambly- 

 pneustes than the low pentagonal typical Microcyphus, which, however, in 

 its 3'oungest stages is also globular and has not yet attained a pentagonal 

 shape. In the interambulacral space the tubercles cover, as a triangular 

 shield, the greater part of each plate, leaving the median sj:>ace and a 

 short length of the horizontal sutures bare from the abactinal pole almost 

 to the actinostome. One large primary tubercle occupies nearly a central 

 position in each plate ; round this are closety arranged smaller tubercles, 

 secondaries, and miliaries, the large central tubercle forming a vertical row 

 of distant ■tubercles. The median sutural pores are small, often wanting. 

 The ambulacral system is proportionally wider than in the other species of 

 the genus ; the poriferous zone is narrow, the pores arranged in a vertical 

 row of pores slightly undulating. In the tuberculiferous part of the ambu- 

 lacra the tubercles are arranged as in the median interambulacral space, 

 only the large tubercle of each plate is placed close to the poriferous zone, 

 forming a regular vertical line; the median space is bare, as well as a part 

 of the horizontal sutures ; the sutural pits are better developed than in the 

 corresponding interambulacral space, and become quite deep towards the 

 actinostome. The abactinal system is small, somewhat raised, quite promi- 

 nent ; the genital and ocular plates have rounded sides ; anal system covered 

 by extremely minute plates ; ocular plates distant from the anal area. Color 

 of the test of these small specimens yellowish-brown, with darker bare me- 

 dian spaces. 



Larger specimens, measuring 25 mm - in diameter, have not lost their ovoid 

 outline. The poriferous zone has become somewhat broader ; the pores are 

 arranged in nearly vertical oblique lines of three pairs ; the whole zone is 

 somewhat sunken ; the arcs of pores are separated by oblique lines of tuber- 

 cles extending from the base of the large tubercle in each ambulacral plate. 



