66 HEMI ASTER MENTZI. 
This concentration of the secondary miliaries seems in some other genera 
to take place in old specimens. This is particularly well shown in large 
specimens of Metalia pectoruUs (see PI. XXI. Fig. 5, Revision of the Echini) ; 
in small specimens measuring not more than half the size of the one figured, 
this structure is very indefinite. In some large specimens of Spatangus 
jmrpureus a slight tendency to a similar concentration of the secondary 
miliaries could also be detected. 
The anal system is transversely elliptical, measuring IG mm. in a specimen 
of 95 mm. in length. In the same specimen, the subanal fasciole is broad, 
enclosing a somewhat heart-shaped area vertically elongate, measuring about 
17 mm. along its greatest diameter. 
* Hemiaster Mentzi A. Ag. 
Hemiaster Mentzi A. Ag. Bull. M. C. Z., VIII., No. 2, p. 83, 1880. 
Lesser Antilles. 170-626 fathoms. 
This small species is characterized by the globular outline of the test, and 
by the narrow, comparatively elongate space included within the peripetalous 
fasciole. It has a larger number of buccal plates than //. gibhoms. The 
tuberculation is coarser and more distant than in that species, more as it 
is in n. zonatns and II. expergUus. As in the latter species, the posterior 
extremity of the test is vertically truncated nearly flush with the rest of 
the test, the anal system but slightly sunken, with a mere trace of an anal 
groove. The test forms over the abactinal part of the anal system a very 
rudimentary hood. This species is also remarkable for the great develop- 
ment of the suckers of the odd anterior ambulacrum. In a specimen 
measuring 17 mm. in length the suckers still retain the prominence thoy 
have in very young Spatangoids. (See the figure of young Brissopsis in 
Eev. Echini, PI. XIX. Figs. 1,2.) This embryonic character is not the only 
one this species retains; its globular form, the position of the peripetalous 
fasciole near the abactinal system, the short comparatively simple peta- 
loid lateral ambulacra, are all features it has in common with the young 
of other Spatangoid genera. In the only other species of the genus of 
which the changes due to growth have been traced {Haniasier cavernosus, 
Challenger Echini, PI. XX". Figs. 7-14), the odd anterior ambulacrum does 
not assume the great prominence it has in the young of this species. In a 
small specimen of II. 3Ienbi, measuring 7 ram. in length, the peripetalous 
