318 ECHINARACHNIUS PARMA. 



comparatively much smaller, the lower surface has become much flattened, 

 the mouth being sunk, and edges of the test raised. There are quite distinct 

 ambulacra! pores, two for each side of the odd ambulacrum, and two and 



three on each side of the other ambulacra. The pairs of pores are pierced 

 between the plates, and are not connected by furrows. Each plate (ambu- 

 lacral and interambulacral) of the test carries as yet but one large primary 

 tubercle; the rest of the plate is thickly crowded with miliaries. In a some- 

 what more advanced stage there was a marked difference iii size between the 

 upper pairs of pores, forming an extremely rudimentary rosette {PL XII. 

 f. .',) of independent pairs of pores not confluent and not joined by fur- 

 rows, additional pores, pierced through the plates, extending towards the 

 ambitus in continuation of the poriferous zone. The larger pores simply 

 radiate fanlike from the apex; there are four pairs in the odd ambulacrum, 

 three and live in the anterior pair, and four and live in the posterior am- 

 bulacra. The miliaries of the plates of test surrounding the main tubercle 

 are larger, and the sutures of the plates more distinctly brought out than in 

 the previous stage. The position of the anus is nearer the ambitus, and 

 when seen from the lower side ( /'/. XII. f. 6), the young Echinarachnius 

 has the same undulating concavity SO characteristic of J'ygaster and allied 

 genera. The outline of this specimen was also somewhat less pear-shaped, 

 and Hatter. In an older specimen, measuring about o.l""" in length ( /'/. 

 XII. f. !)). the test had become quite flattened, the mouth was slightly 



sunken below the raised r<\^- of the ambitus, the outline i e pentagonal, 



the vent placed nearer the edge, and we have the first appearance of pores 

 arranged so as to form a distinct rosette, connected by furrows in the part of 



the rosette nearest the middle. As in the preceding Stage, there art' addi- 



ditional pairs of pores pierced between the ambulacra! plates extending 

 towards the ambitus in continuation of the rosette. Each plate now carries 

 from three to six primary tubercles, according to its size, thickly crowded 

 round with miliaries. The anal opening is closed by a single plate (PL XII. 

 J. 11); the madreporic body i^ quite distinct, and very minute pores can be 

 traced in the indistinct ambulacral furrows of the lower side. In specimens 

 measuring G. mm - the rosette is more prominent (PL XIT. f. 1<>), the pores 

 being all connected by furrows; the plates of the test are uniformly covered 

 by primary and miliary tubercles, the sutures of the plates are less distinct, 

 and four small additional anal plates have appeared (PI. XII. f. 1 / ) at the 

 marginal i'A^c of the anal opening. In still larger specimens, measuring 



