Asteroidea of Portuguese East Africa. 57 



The following is a description of the largest specimen (Figs. 1-4). 

 The plates are all arranged in definite rows ; they are markedly 

 convex, and the axis is transverse. The following series may be 

 distinguished : — One mid-dorsal series ; two sub-lateral series ; one very broad 

 sub-ventral series. Several of the plates appear as if composed of 

 segregations of smaller dome-like plates. 



The median row, or mid-dorsal series, terminates in a larger plate at 

 the junction of the arm and disc. Between these five plates, which are 

 arranged pentagonally, five others are disposed symmetrically, while in the 

 centre of the disc there occurs a single plate of a size similar to the 

 others. The arrangement of the tubercles on the surface of the disc is 

 markedly symmetrical. 



The sub-lateral rows on opposite sides of adjacent arms are continuous 

 through the angle ; this series does not extend to the tip of the arm, 

 but is terminated abruptly by the union of two sub-parallel poriferous areas. 



The plates of the sub-ventral series are more or less rectangular in 

 shape ; they are densely covered with coarse regular granulations which 

 are interrupted by a furrow, running medianly to half-way from the ventral 

 edge of the plate. 



The poriferous areas lie in six longitudinal rows, three on each side of 

 the arms ; the average number of pores in each group is about fifteen ; the 

 areas are distinctly larger than the corresponding plates. On each side of 

 an arm the upper sub-lateral series of plates does not extend to the tip ; 

 consequently the poriferous areas which are otherwise separated by these 

 plates are confluent in this region. Occasionally these larger poriferous 

 areas are united transversely by small and almost inconspicuous lines, 

 bearing pores. 



The madrepore is simple and distinct, and recalls the structure of the 

 coral Fungia. It is larger than the plates of the dorsal surface, and lies 

 in the angle formed by the dorsal row of plates and the upper sub- lateral row. 



The ambulacral armature is bi-serial ; the inner row consists of large 

 and small alternate spines, four or six on each plate (five may occur) ; they 

 are blunt, sub-triangular in shape, and interlock. The spines of the outer 

 series are larger, more distant, vertical, conical, and occur in pairs or threes 

 on each plate. 



In both series there is a tendency towards an alternation in these 

 numbers — e.g. (1) inner series, four and six on alternate plates ; 



(2) outer series, two and three on alternate plates ; 

 but from about halfway from the mouth to the tip of the arm the number 

 tends to diminish and the rows lose their regularity. Occasionally a single 



