014 SCHIZASTER VENTRICOSUS. 



Schizaster ventricosus 



! Schizaster ventricosus Cray, 1851, Ann. Mag. N. II., VII. p. 133. 



This species is intermediate between the species of the group of the genus 

 to which S. fragilis and S. Philippii lielong and that formed by S. canaliferus 

 ami S. gibberulus. It has the comparatively elliptical outline and subcehtral 

 apical system of the former, with the more deeply sunken lateral ambulacra, 

 broad anterior groove, the angular peripetalous fasciole, and the four genital 

 openings of the latter group. 



Test thin ; outline from above broadly elliptical, angular anteriorly. Api- 

 cal system subcentral, posterior ; vertex immediately behind the apical sys- 

 tem, which is situated in tin- flat sloping space formed by the spreading of 

 the median ahactinal part of the interambulacra, which narrow the abactinal 

 part of the petals almost to a point, forming a slight angle with the general 

 direction of the lateral petals, as in S. canaliferus and S. gibberulus. The 

 two posterior genital openings are large, round ; the anterior small, forming 

 an irregular rectangle. The posterior petals are concave outwardly ; the an- 

 terior only arch outwardly at the extremity. This species is remarkable for 

 the great breadth of the lateral ambulacra. The odd anterior ambulacrum 

 is placed in a deep. Hat. rectangular groove, with steep sides, forming a high 

 keel in the median anterior interambulacra! space, extending nearly from the 



apex to the peripetalous fasciole. where the keel is lost. The peripetalous 

 fasciole is broad, angular, extremely broad at the extremity of the anterior 

 lateral petals, re-entering in the median interamhulacral spaces. 



The broad posterior extremity is nearly vertically truncated, forming a 

 broad, Hat, posterior extremity, in which is placed the comparatively small 

 anal system, covered by plates decreasing uniformly towards the anal opening. 

 The lateral fasciole runs obliquely to the ambitus from the middle of the an- 

 terior ambulacra towards the posterior extremity. The posterior extremity 

 of the actinal plastron is lost in the rounded posterior edge of the test. The 

 tuberculatum within the peripetalous fasciole is coarse, closely packed in all 

 the interamhulacral spaces, except the odd posterior one. 



DisI Length Length Width 



Long. Trans. Ap. Sv-t. Post l.-it. Ant. Lai Ant Odd 



Diani. Diam. Efelght. Post. Edge Amb. Pet. Amb. Pet. Amb. 



69. 60. 43. 32. 10. 27.5 8. 



Feejee Islands ; Philippine Islands ; Siant. 



