G6 HEMTASTER 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 pectoralis (see PL 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 

 purpureas a slight tendency to a similar concentration of the secondary 

 miliaries could also he detected. 



The anal system is transversely elliptical, measuring 16 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 //. gibbosus. The 

 tuberculatum is coarser and more distant than in that species, more as it 

 is in H. zonatiix and // expergitus. 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 they 

 have in very young Spatangoids. (See the figure of young Brissopsis in 

 Rev. Echini, PI. XIX. Figs. I, 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 [Hemiaster cavernosus, 

 Challenger Echini, PI. XX 1 . Figs. 7-11). the odd anterior ambulacrum does 

 not assume the great prominence it has in the young of this species. In a 

 small specimen of //. Mentzi, measuring 7 mm. in length, the peripetalous 



