MACROPNEUSTES SPATANGOEDES. 65 



;11V dosed at the extremity, the am. Tier pair is considerably larger thau 

 the posterior pair. The outer rows of pores are the largest in both lateral 

 petals. The pair- of pores are sunken. The odd anterior ambulacrum con- 

 sists of lines of single pores, one for cadi ambulacral plate Apical system 

 compact, with four genital openings and Bmal] madreporic body. 



The roosl 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 Snd to be the case also in some specimens of this spe- 

 cies of Macropneustes, En others, the anterior par! of the fasciole beyond the 

 extremity of the anterior petals becomes indistinct or disappears. In still 

 other specimens, the posterior pari of the fasciole across the odd interambu- 

 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 lew such disconnected 

 V-shaped areas take the place of the fasciole; as these become less numer- 

 ous and more indistinct, the fasciole disappears completely. These \ -shaped 

 areas form as it were Becondarj posterior and lateral branches of the peripet- 

 alous fascioles, similar to the anterior hand- observed by Troschel in Tripylus. 

 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 tin- 

 crowded miliary tubercles covering that part of the test. In some of 

 the specimens the miliaries of the lateral ambulacral and interambulacral 

 area- below the peripetalous fascioles show a tendency to he 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 hare 



Butural bands characteristic of soi if the genera of Cidaridae, Arbaciadao, 



Temnopleurid®, and other Echinoids, are not the first trace of fascioles. So 

 that we may consider the concentration of the miliary and secondary miliary 

 tubercles mi the edges of certain plates, or in (he centre, so a- to form bare 

 sutural lines or bands along certain part- of the test, either in the ambula- 

 cral or interambulacral area-, as the first indication of the formation of fasci- 

 oleB, or a- rudimentary or disconnected fascioles, 



