MACEOPNEUSTES SPATAXGOIDES. 65 
are closed at the extreuiit}-, the anterior pair is considerably larger than 
the posterior pair. The outer rows of pores are the largest in both lateral 
petals. The pairs of pores are sunken. The odd anterior ambulacrum con- 
sists of lines of single pores, one for each ainbulacral plate. Apical system 
compact, with four genital openings and small raadreporic body. 
Tlje most interesting structural feature of this genus is the composition of 
the peripetalous fasciole, and the light which this throws on the possible 
origin of the fascioles as a whole. As is well known, in Macropneustes the 
peripetalous fasciole forms a clear, simple narrow band around the extremity 
of the petals. This we find to be the case also in some specimens of this spe- 
cies of Macropneustes. In others, the anterior part of the fasciole beyond the 
extremity of the anterior petals becomes indistinct or disappears. In still 
other specimens, the posterior part of the fiisciole across the odd interarabii- 
lacral area widens, forming elongated V-shaped areas : sometimes there are 
two or three such areas. In other cases a similar structure extends across 
the lateral ambulacra. In other cases, again, only a few such disconnected 
V-shaped areas take the place of the fasciole ; as these become less numer- 
ous and more indistinct, the fasciole disappears comjjletely. These V-shaped 
areas form as it were secondary posterior and lateral branches of the peripet- 
alous fascioles, similar to the anterior bands observed by Troschel in Tripylu.s. 
Across the anterior ambulacrum there are sometimes no less than six or 
seven such secondary fascioles, some of the upper branches uniting again 
with the main fasciole, others extending parallel to the ambitus across the 
ambulacra into the lateral ambulacra, where the extremities die out in the 
crowded miliary tubercles covering that part of the test. In some of 
the specimens the miliaries of the lateral ambulacral and interambulacral 
areas below the peripetalous fascioles show a tendency to be crowded towards 
the lower edges of the plates, thus forming indistinct V-shaped areas resem- 
bling somewhat the V-shaped areas of the secondary fascioles, but made up of 
course of larger tubercles. This suggests the question whether the bare 
sutural bands characteristic of some of the genera of Cidaridas, Arbaciadai, 
Temnopleurid£B, and other Echinoids, are not the first trace of fascioles. So 
that we may consider the concentration of the miliary and secondary miliary 
tubercles on the edges of certain plates, or in the centre, so as to form bare 
sutural lines or bands along certain parts of the test, either in the ambula- 
cral or interambulacral areas, as the first indication of the formation of fasci- 
oles, or as rudimentary or disconnected fascioles. 
