AEROPE FULVA. 195 



fig. /). Near the actinostorne the posteiior lateral ambulacra are nearly 

 bare (PI. 61, fig. 6), they are only covered witli a few niiliarie.s and a few 

 small secondary tubercles, except near the ambitus (PI. 02, fig. S), where 

 the plates become as closely tuberculated as are the inter.'imbulacral plates 

 on the actinal side (Pis. 61, figs. /, 2; 62, fig. 7). The labium is ycry 

 narrow, lozenge-shaped, with five primary tubercles in the anterior half of 

 the plate. The anterior lateral primordial plates are pentagonal, short, and 

 carry two primary tubercles. The lateral posterior primordials are turned 

 backwards at a right angle, extending posteriorly more than the whole length 

 of the first actinal plate of the posterior lateral ambulacra (PI. 61, figs. /, 6). 

 The actinostorne is longitudinally elliptical with rounded edges, the phyl- 

 lodes are limited to the first actinal ambulacral plate (PI. 61, figs. J, 6). The 

 coronal plates are slightly imbricated towards the actinostome in the ambu- 

 lacra, and away from it in the interambulacra. 



The peripetalous fasciole (PI. 61, figs. 1-3) is not as broad as that of A. 

 rostrata ; it forms an angle in the median anterior interambulacrum, near the 

 ambitus, passing then nearly vertically round to the actinal side of the test 

 (PI. 61, fig. 1), and crossing the anterior part of the odd anterior ambulac- 

 rum in a straight line. 



The lateral ambulacra do not differ except in length ; their plates are 

 remarkably uniform in size inside of the peripetalous fasciole (PI. 61, fig. J), 

 and above the ambitus as far as the anal system, though on the actinal side 

 the plates of the odd ambulacrum and of the posterior lateral ambulacra 

 become very elongated (PI. 61, fig. /), those of the anterior lateral ambu- 

 lacra being less so, and those of the posterior lateral ambulacra attain the 

 greatest longitudinal extension; they increase gradually towards the ambi- 

 tus, those of the posterior extremity of the posterior lateral ambulacra are 

 much larger along the sides of the test as they pass from the ambitus to 

 the actinal side. The plates of the odd ambulacrum are wider and narrower 

 than those of the other ambulacra. 



There are three genital plates with four large genital pores (Pis. 61, 

 fig. ,'; 62, figs. /, 3) ; all of these in one case (PI. 62, fig. l) encroach upon 

 adjoining plates, Fig. 281, in the other upon three and upon ono of the 

 anterior oculars (PI. 62, tig. ^). The madreporic body extends over one 

 genital plate, and the stone canal, when seen from the interior. Fig. 282, 

 projects like a hood well over the adjoining genitals, ending on the right 

 posterior ocular (PI. 62, fig. 3). 



