326 CARDIASTER. 



The anteal and antero-lateral ambulacra are short, lanceolate and nearly vertical ; 

 the postero-lateral long, ascending obliquely forward, and conjointly forming an arch 

 which encloses the posterior truncated border with the circular vent about half way up the 

 total height of the test (see Table). The plates of the ambulacra are large and broad, 

 each equal to as much or rather more than half the height of an interambulacral plate. 

 In a rather large example of this species there are seventeen dorsal plates in each vertical 

 row of the anteal ambulacrum, about fourteen and thirteen respectively in the rows of each 

 lateral ambulacrum, and seven in each vertical row of each lateral inter-ambulacrum 

 (PI. LXXI, fig. 1 c). These plates all bear minute scattered primary tubercles, with 

 myriads of interspersed granules (PI. LXXI, fig. 1 li). 



The upper surface is convex, and more or less arched throughout ; the highest point is 

 in the anterior third, from whence it gently declines towards the posterior border (figs. 1 c 

 and 3 a). The apical disc is closely wedged in between the other plates of the test, and 

 often distinguished with difficulty; it is situated about the centre of the test, rather 

 nearer the anterior border, and is narrow and extremely elongated (fig. 1 e) ; the ovarial 

 plates being placed in line behind each other, and four are perforated. The ocular 

 plates are very small, and can only be discerned by the aid of a magnifying lens. The 

 madreporiform body is very small and indistinct. In some flint casts the four ovarial 

 holes are seen, and the pairs of pores in the poriferous zones very well shown (fig. 2) ; 

 their courses are much better traced out in such moulds than in specimens with the test 

 preserved. 



From the posterior side of the apical disc to the upper margin of the vent a carina 

 more or less acute is developed (fig. 1 a), this ends in a beak -shaped process which 

 overhangs the anal aperture. 



The under surface is slightly convex, and a little angular along the median line, 

 without any concavity around the mouth, which occupies a position near the anterior 

 extremity, about one fourth of the length of the test from the margin, which in the 

 region of the anteal ambulacrum is slightly sinuous (fig. 1 b). The oral aperture is 

 roundish or ovate, the fore lip is depressed, and the hinder lip turned and elevated, but 

 not overlapping. 



The vent of an oval form occupies an elevated position in the posterior border (figs. 

 1 (^and 3 a). This aperture was defended by a series of small plates, eight polygonal 

 calcareous pieces forming the outer, and ten smaller pieces the inner circle of the lid, so 

 that the periprocte was entirely closed with the exception of a small central aperture for 

 the passage of the rectum. I have given an accurate drawing of these anal ossicles iti 

 situ for shutting up the periprocte in fig. 3 b. 



This beautiful little Urchin likewise possesses a band of minute granules towards the side 

 margins of the ambitus, forming thei'e a fasciole like a Cardiaster ; for this reason 

 it is now removed from the genus Ananchytes, where it was placed, but in which no 

 fascioles exist, into the group which possesses this granular band along the margin of the 



